I'm not against spur stopping or for it or anything like that. I just want to say to anyone that says a horse doesn't know any different is wrong, IMO.
From what I know and believe to be true, horses are born with a natural drive line and have it the rest of their lives. if you went up to a wild horse, given you could get close enough, and smacked it in the rump or anywhere behind their withers it will run forward, if you hit it on the chest, it will step backwards, even just slightly before running off. It is in their nature. Like if someone pokes you in the chest you step back, or some one kicks you in the butt you step forward, its a natural thing.
I'm not saying training a horse to spur stop is any more difficult than to train a horse to stop with the rein because horses are trained to do all sorts of things out of their nature.