My horse will only stop well when I have him on the bit. When he is he'll stop on 'whoa' or when I sit deep and barely squeeze the reins. When he isn't on the bit, or when someone else is riding him and they're not as good a rider, he's difficult to stop. He braces on the bit for a couple strides and then he'll come to a rocky stop. Is this because he's not on the bit and therfore not listening, or is there someway I can get him to stop no matter what?