This is what I have always done. If I need the horse out of my space or what have you that requires that I get physical with them I use the end of the lead and smack them in the shoulder. Even if they try and bit I never hit the horse in the head or face. I have found it works just as well to hit their shoulder as it dose their face. I also find that if a horse is in my space and I want them out of it. I put pressure on them by hitting them in the shoulder with the lead and walking towards them and use a very stern voice. Do this once or twice and all you need is the stern voice most of the time. Having handled a lot of stallions I pick my badles carfully and I never loose.I was not okay with her slapping the horse in the face to get it to 'yield' the forehand, in my opinion the better way to get a horse to do that is go for the shoulder.
I also employee a 3 second rule. IF I can not punish the horse with in 3 seconds of what ever it is they did then I do not do it. The punishement what ever it may be only last 3 seconds and then that is it. I give them a moment to think about it. I have yet to have a horse who did not learn quite quickly this way. Make them think they are going to die with in those 3 seconds and then it is done.