I'm going to jump in and say that whatever works for you is just fine - if it works. While I've done (and would do again if necessary) is to discipline a horse that is acting up on cross ties or to my trailer. Sometimes that will be a knee in the ribs if I'm close or it may be some "thinking" time if I'm not.
We can not do to our horses anywhere near what other horses can do to them unless we let our tempers get in the way. I never kick my horses in the legs but I will put a knee in their barrel. It works and is not abuse - it is what they understand.