What does Anderson say about using the fence or wall to help teach neck reining?

Clinton Anderson uses the fence as a training tool in neck rein development for a specific mechanical reason: when a horse is ridden along a fence on its right side and the rider applies the left neck rein asking for a right turn, the fence prevents the horse from continuing straight and provides a physical reinforcement of the rein's meaning without the rider needing to add direct rein. The horse turns right because the combination of the neck rein and the fence makes it the obvious response. Anderson teaches riding along the fence on a loose rein first to confirm the horse is comfortable working close to it, then applying the neck rein at the moment the horse's path would naturally need to follow the fence's curve. The fence removes the option of going straight, which means the horse's correct response to the neck rein — turning — is the only comfortable option available. Over repetitions, the horse begins turning from the neck rein before the fence becomes necessary, because it has learned what the rein means. He uses this technique specifically for horses that understand the direct rein but are slow to transfer that understanding to the neck rein. The fence-assisted session fills in the gap between what the horse knows and what it is being asked to learn, giving it a physical context in which the neck rein cue and the correct response are clearly connected. Anderson also teaches progressing away from the fence as soon as the horse is responding correctly — a horse that only neck reins along the fence has learned to use the fence, not the rein. The fence is a teaching aid, not a permanent fixture, and the transition to open-space neck reining should happen as soon as the horse demonstrates consistent response.