What does Clinton Anderson say about a horse that rears under saddle and how is it corrected?

Clinton Anderson identifies rearing as one of the most dangerous behaviors a horse can develop and teaches that it requires a specific, confident, and immediate response every time it occurs. He also teaches that prevention through groundwork is far more reliable than correction after the fact, and that most rearing horses have a specific deficiency in their forward response that created the behavior. Anderson's explanation of why horses rear is direct: a horse rears when it wants to go backward or sideways but is prevented from doing so by the rider's hands. The horse's natural response to confinement that blocks backward movement is to go up. A rider who consistently holds too much with the hands, who blocks forward movement repeatedly, or who has a horse that has not learned to move freely forward is creating the conditions for rearing. The primary prevention is establishing a genuine, immediate forward response on the ground and carrying that forward response into the saddle. A horse that moves forward from the lightest leg aid without hesitation and maintains forward movement without constant driving has removed the root cause of most rearing. For a horse that rears in the moment, Anderson teaches leaning forward over the horse's neck rather than leaning back, which removes weight from the hindquarters and reduces the horse's ability to rear higher, and immediately pushing the horse forward with both legs the moment it comes down. The horse is never allowed to stop after a rear — it must move forward immediately, because stopping rewards the behavior. Anderson also teaches a specific prevention technique for horses he knows are likely to rear in a given situation: before the situation is encountered, transition to a trot. A horse that is trotting cannot rear effectively. Knowing this, Anderson has riders approach any situation where rearing is expected — a gate, a barn, another horse — at a trot, which removes the opportunity for the behavior to develop.