These exercises are sometimes classified with "dressage" training and some riders are intimidated by them, but they are essential skills for a safe, reliable trail horse. They are not really very difficult and, at their basic level, are relatively easy for almost any rider to teach to a horse.
TURN ON THE FOREHAND:
Horses travel down hill most safely when their hindquarters track directly behind their shoulders. Unfortunately, most horses tend to drift off to one side or another with their haunches when they are ridden down hill. To overcome this problem, you should teach your horse to position his hindquarters to one side or the other in response to your signals. When you have control over his haunches you can keep him straight going downhill.
To teach the turn on the forehand, start on the ground, standing next to the horse. Apply steady pressure with your fist to the horse's side, just behind the girth where your leg would hang if you were mounted up. At the same time, using one rein, turn the horse's nose sightly towards you. Keep the horse from moving forward. His haunches will automatically swing away from you. Ask for one step, then two then three or mor to the side with the hindquarter only. Then repeat the process on the other side or the horse. Continue to work from the ground for a few lessons until the horse willingly moves his haunches over with very little pressure from your fist, only sightly tipping his nose toward you. Next, try the exercise from the saddle, this time using pressure from your leg, slightly back of the position it would normally fall, in place of the fist. Push the hindquarters first to one side, then to the other, keeping the horse from moving forward as you do. Ask for one step, in each direction, then stop and praise the horse. The next time you ride, ask for two or more. Sometimes a very dull horse will learn better if you have a friend stand on the ground and push with his fist as you use your leg until the message sinks in.
The turn on the forehand gives you control over a horse's hindquarters. Using it, if a horse starts to drift to the left with hind hindquarters going down hill, you can push his haunches back to the right until they are straight under him again. It is the first of a series of exercises that move the horse away from leg pressure in various ways.
TURN ON THE HAUNCHES:
The turn on the haunches is a useful exercise for teaching the horse to work with his hindquarters under him and it makes him more maneuverable in tight spaces on the trail. It is also a building block for the side-pass, which is an essential trail maneuver.
To teach the turn on the haunches, again start on the ground, standing next to the horse. This time you are going to be moving his forequarters away from you, with his hindquarters staying in place. Use one hand on the rein on the side away from you to turn the horse's head in that direction. Place the other hand over the girth area on the side toward you, forward of where your leg would normally hang in the stirrup. Apply steady pressure with your hand, moving the front of the horse over one step. Try to keep him from backing or stepping to the side. If the horse is confused by this action, it sometimes helps him understand what you want if you push against the side of his neck about half-way between his head and shoulder, to literally shove his front end away from you. Practice until he will easily take a step away from you with his front feet, to either side. Then increase the number of steps until he will step most of the way around his hindquarters, turning on his hind feet. He may take a step to the back or to the side as he turns. Don't worry about that — it is natural and a way for him to keep his balance.
Mount up, and ask for the turn on the haunches, starting with a single step from the front legs. Use your direct rein to tip the horse's nose in the direction you want him to go, use the neck rein across his neck to cue him to move his neck and shoulders away from pressure, restrain the horse lightly so that he does not try to go forward, and use definite pressure with your leg on the side you want him to move away from, pushing with it just forward of the position you used to make him move his haunches over. With a little practice, he will step to the side with his front feet only, turning around his hindquarters. Practice until he can move a couple of steps in each direction, easily and with no resistance. For trail work, you do not need to teach a pivot on the hind feet, but you can probably figure out how to do that exercise from this simple beginning. Do not try to pivot a horse that is shod with caulks in the back, this will put a lot of torque on his hind legs. It is probably best if you work at this exercise not as a true pivot, but as a moving turn on the haunches, allowing the horse to take small steps to the side with his hind feet, similar to the type of exercise used in dressage, since that type of turn puts less stress on the horse's legs.
Once the horse has learned the turn on the forehand and turn on the haunches, you can teach him to put them together into the maneuver called a side-pass. In this exercise the horse moves directly to the side, away from your leg and neck rein pressure. This is very useful on narrow trails above steep banks to keep the horse safely away from the edge. It is necessary for opening gates from the saddle. It is also nice to use this exercise to move around trees or away from other horses if they are crowding too close on a group ride.
You can teach the side-pass from the ground, combining the cues you used for the turn on the haunches and the turn on the forehand, or you can skip that step (since the horse can perform both of those exercises mounted by now) and teach it from the saddle.
To do the side-pass to the right, push with your left leg slightly to the back of where it would normally fall to move the haunches over, then, using your neck rein to push his neck and shoulders to the side and lightly restraining the horse so that he does not move forward, ask him to move his forequarters over as well. You may need to reinforce this with a leg cue forward at the girth area. The horse will move to the side, jerkily, first with the haunches, then with the shoulders. Stop and praise him, then try again, this time, giving the cues for moving the haunches and the shoulders almost simultaneously. He should move over one step, perhaps not smoothly, but still moving over. Practice until you can give the cues to move over simultaneously, with your leg held over the girth centered between the two positions used for moving the haunches alone and the forehand alone. Lean your body sightly in the direction you want to go, and be sure to keep up leg and rein pressure as you move to the side. Practice in both directions, a few steps at a time, until the horse moves easily away from your leg and rein, "yielding" to the leg. You may find that the horse moves very easily one way and hardly at all the other. Practice to the "bad" side until he moves well both ways. If he acts confused, go back to the simpler turns on the forehand and haunches and start over. Keep him calm, slow and relaxed. The side-pass is a useful tool for safe trail riding, but it is useless if the horse rushes sideways in a panic away from your cues. Controlled, relaxed response is what you are trying to achieve with this and all trail training exercises.
Once the horse has mastered the side-pass, you can also teach him the exercise called a "leg yield", in which he moves forward and to the side at the same time, his body straight (not curved toward the way he is going or away from it). This is a useful skill for trail riding, not a dressage move. To do a leg yield, drive the horse forward with leg pressure n the walk, then as he is moving, as for the side pass, discontinuing any retraining action from the reins, using the neck rein to keep up the sideways motion. The horse should move forward and to the side. Try to make the forward motion at about a 45 degree angle, keeping the horse's body straight. You will have to use some leg and rein action to keep this exercise going, but with practice you should be able to move easily forward and to the side. It helps if you set out a marker (one of your cones) to give you a target to move toward as you practice. Don't worry if you are not perfect at this exercise — it is useful but not absolutely necessary for trail riding.
The last and most important gymnastic exercise your horse must learn before he is safe on a trail is collection. This is not moving along slowly with his head and neck in a "tucked" position — it is working with his hindquarters under him, balanced to the rear, carrying your weight and his own more with his strong haunches than with his shoulders. It is the position of balance under a rider that is most efficient for carrying weight, and safest for going up and down hill. To be collected under a rider, a horse must be taught how to round his back and use his hindquarters as freely as he would if he was on his own. This is not the same thing as setting his head. Often horses that have had their heads "set" in bitting rigs are incapable of rounding their backs because their muscles are stiff and their bodies are unresponsive to leg pressure.
The best way to start to teach collection to a Fox Trotter is from the flat walk. Ride in an energetic flat walk with two hands on the reins. Using frequent, light tremors on the reins ask him to take slightly shorter steps, still keeping up his forward momentum. Keep light contact with his mouth through the reins, and keep up leg pressure to keep him moving forward, but allow him to reduce his long striding flat walk to shorter-stepped gait of about the same speed. His head and neck will rise a bit and his nose will come in toward the vertical. Let the horse learn to hold himself in this position as a result of the pressure of your legs and the gentle restraint of the bit. Do not force his head into a tucked position! The idea is to push him together with the action of your legs, not to force his head into position by pulling with your hands.
Ride the horse in this new position for a few steps, then let him relax into a slow, ordinary walk by releasing both bit and leg pressure. Repeat the exercise. For increasing intervals over the next few weeks, practice this exercise until you can almost halve the length of his steps in the walk. Do this without upsetting him or hanging on his mouth, still keeping up the forward momentum of the flat walk. It sometimes helps to stop from the walk, back the horse a few steps, then continue on. This brings the horse's hindquarters under him and improves the flexibility of his body. Always alternate collected work with time at a stretched out ordinary walk to relax muscles that may become cramped as he learns to travel in this new way. Give him time to get in shape.
Work at a collected walk helps the horse learn to use his hindquarters so that you can keep him from stringing out and perhaps falling going down hill. Shortening his steps allows you to guide him through tricky footing (rocks, logs) on the trail. Don't worry, his stride will not be permanently altered if you teach him to shorten it through collection. You can always push him back out in a reaching flat walk when you want it.
Once your horse has mastered collection in the ring, take him out and ride him up and down some gentle hills. Let him walk slowly up hill, then ask him to collect a little going down the same gradual grade. Lean forward to lighten the load on his pushing hindquarters going up hill. Sit in the middle of the saddle, leaning very slightly back going down, to help him shift his weight to his hindquarters and avoid over-burdening his front legs. When he can handle gradual hills, try riding him up and down steeper ones, keeping him collected with tremors on the reins as you go down. Shorten his steps going down hill, keeping his hindquarters squarely behind his front end. Keep him relaxed and focused on where he is going. He should never rush up or down hills with you, but take all steep terrain in stride, staying balanced under your weight.
**Advice on slides: Once your horse can handle a steep hill, keeping collected with his hindquarters under him, you may be tempted to try him on a slide. This is not a very smart thing to do on the trail — a horse can easily fall and injure both himself and his rider on a slick slide. It is also devastating to the natural terrain to ride down slides. Managers of most public lands discourage them, and private landowners are not very fond of them either. Do your horse and the environment a favor and skip the slides. If you need to go down a very steep hill, go in gradual zig zags. Better yet, look for a less steep way down.
If you have done basic training for trail at home, your horse should be able to neck rein around stumps, pick his way through downed timber, walk through brush, and back out of tight corners. He should be safe on ledge trails, able to keep balanced going down hill, and easily maneuverable in groups. With only a little practice, he should be a pleasure to ride on the trail.