For example, when you’re heeding a horse on the ground in an arena and you want him to canter off on his left lead, you’ll "skip"along keeping your left leg ahead of your right and you’ll turn your shoulders so they create a feeling of "open" and "forward" in the direction you want him to go. In the beginning, since he doesn’t yet understand what you’re showing him, you’ll probably extend your right arm out parallel to the wall and wiggle your whip to make a little fuss and create a little more activity in the horse. If he still doesn’t get the feel of what you want, you might drop back a little further toward his hip or move in a little closer to him or whatever it takes for the light bulb to go on over that particular horse’s head.
Once he understands what you are showing him, you can ask for the left lead canter and expect a more immediate response. You won’t need quite so many pressures to create the feel in the horse of the shape that you want. When he’s consistently giving you the left lead canter whenever you ask for it, now you can just tell him that’s what you want with only the beginning of that little skip. That becomes enough to remind him of the full feel of the shape. It has become something like a signal but if the horse gets rusty, you can just go back to using a full corridor of pressures that ask for "canter" until he associates just one part of the corridor with the "canter" shape again.
There is going to come a time when you know the horse fully understands the shape you want and you tell him that’s what you want but, for whatever his reasons that day, he decides not to listen to you. Then you have to enforce. You might also be starting to work the horse at the higher levels of his sport and now you want him to do what he’s already doing but to do it with more energy or a little more precision. Then you have to enforce.
Enforcing means using your aids with greater emphasis. It means disciplining the horse in the spirit of the word "disciple". The teacher makes a point by calmly interrupting something that’s going on or by stressing an aid as it is applied. Enforcement is not punishment. Punishing a horse is something riders do when they’ve made a mistake and they feel guilty and they want to make themselves feel better about it. It’s like someone throwing a swear word into the conversation because they’ve run out of other vocabulary. It’s an action that disrupts the communication between the horse and its rider and breaks up any corridor of aids they had going. The horse doesn’t learn a thing except that the rider is being illogical.
Whatever you do to enforce should not raise the horse’s excitement level. Enforcement should bring the horse’s attention to a particular part of a corridor of pressures without losing the feel of the whole corridor. If you use one aid too "loudly", the horse’s attention goes to that aid and he loses the feel of the corridor. For example, if your good ole boy horse ignores you when you first tell him to canter so you start right out the next time by telling him to canter with a touch of spur, you are being too "loud". But if you touch the horse with a spur at the end of a leg squeeze just as you feel the horse is choosing to ignore the leg, that’s a horse logical enforcement.
Timing within the whole corridor of aids is critical in enforcement. Let’s say you’re coming up on a jump and you feel the horse just starting to ignore your leg pressure and lose his impulsion. You just maintain all the aids you’re already using to create the corridor of pressures that lead up to the jump but you add a little tap with the crop to enforce them and prevent a refusal. If the horse refuses the jump and then you show him the jump and spank him with the crop, that’s punishment. It’s not going to enforce a thing.
Being ready to enforce the things you tell a trained horse to do might mean having the right level of physical fitness to properly apply the aids. Or it might mean adding a crop or whip to your corridor of aids to help amplify one part of the corridor. Some people get all hung up trying to classify things as "natural aids" versus "artificial aids." If it’s physically a part of you like your hands or your seat or your legs then it’s natural. If it’s something you attach to yourself or your horse like a whip or a spur then it’s artificial. And some people get into all sorts of moral dilemmas about whether or not it’s OK to use one kind or the other.
When you’re enforcing, it really doesn’t make any difference whether you’re doing it with a body part you grew yourself or something manufactured that you bought at the tack shop. The important thing is how you use it. Whips and spurs are no more abusive or exciting than your hands or your seat or your legs. You can use your hands or your legs in an abusive way and you can use a whip or spurs to convey the subtlest communication. It’s all a matter of degree and timing and coordination of that individual aid within a whole corridor of aids that communicates a shape and a direction, and a rhythm and a lot of other things to the horse.
The key thing is that whatever you do to enforce what you’ve told the horse to do should not raise his excitement level. Enforcing with dramatic pressures creates activity and makes it look like something is happening. When you’re using nuances, it doesn’t look like much is going on. Good training is boring. If the people watching you don’t feel like anything exciting is happening, then you’re probably doing it right.