What does Warwick Schiller say about a horse that is barn or gate sour specifically at the mounting location?

A horse that behaves well everywhere except at the specific location where mounting occurs — swinging its hindquarters away, walking off, becoming tense — is something Warwick Schiller addresses as a location-specific conditioned response. The horse has learned to associate the mounting location with something it wants to avoid, and the behavior is its attempt to prevent what follows. Schiller's diagnosis begins with investigating what the horse is trying to avoid. In many cases it is simply the work that follows mounting — the horse is not mounting-sour, it is work-sour, and the mounting location is where work reliably begins. In other cases the horse has a pain association: the saddle that fit poorly, the back that was sore, the girth that was tightened too quickly — and the mounting location is where that pain began. In a smaller number of cases the association is with a specific frightening event that happened at or near that location. For the work-avoidance horse, Schiller's approach is to change what the mounting location predicts. He will mount the horse at that location, sit quietly for several minutes without going anywhere, then dismount and let the horse stand. He repeats this across multiple sessions until the mounting location no longer reliably predicts the beginning of work, which removes the horse's motivation to prevent the mounting. For the pain-association horse, the priority is identifying and resolving the pain source — saddle fit, back soreness, dental issues affecting the bridle — before any behavioral work. A horse that is avoiding mounting because it predicts pain is being rational, and resolving the pain resolves the behavior far more reliably than training through it.