Hmm I slap a horse on the rump and say "over" quite a bit at the riding school, but that's because they are riding school horses so are used to being mucked about by people who don't know what they are doing. As a result this is the only thing they tend to understand when you want them to move to the other side of their loosebox.
I will smack them on the nose if they bite me or are misbehaving, how hard I do it depends on the level of the threat.
I often use force on a 17HH horse at the riding school to get him to move over otherwise I am only a mere fly in comparason to him and he likes to stand his ground. When I say 'force' I mean leaning against him will all 8st of me (not much). And ocasionaly the odd elbow in the chest, ribs. But nothing that would hurt him or damage him long-term.
The only time I have used what I consider to be 'real' force is when I was riding a welsh mountain pony. He is only 3 and was broken in badly so is badly behaved. The only way I could get him to listen to me was a harsh slap on the rump a few times with the riding crop. By harsh I mean rasing my hand until it was about level with my shoulder and then using a harsh downward motion. The resounding 'thwack' scared him more than the pain I think as all I need do now is hit my boot to make a similar noise and he gets the message. Ocassionaly he needs a slap on the rump.
Is any of this wrong? Please let me know, but at a riding school the horses are used to being ridden by people who don't know what they are doing and as a result may have got into bad habits.