He did try and bite me once, because I was taking too long with food. I ran straight back at him, waving my arms and chasing him backwards. He pinned his ears and reared, so he really got chased. I spent about 10 minutes chasing him around the paddock and he's never tried it again.
Thats exactly the same as a friend of mine. When she gets a new horse, or is training something that pushes the boundaries she uses a similar approach. To start with she will raise her voice and make her body language big. If they repeat the action the same thing will happen. If they do it a third time (as in try to bite, kick or something that would put her in physical danger) then she will run 'at' them, hands waving, shouting etc if she has something she can crash about to make a loud noise she does. However she makes sure she reacts as soon as the horse threatens her. The moment the horse stops threatening her, she stops, continues what she was initially doing and will then go and make friends with the horse again a moment later.
Like someone (chev?) mentioned earlier, similar to a mother with a foal.
If the horse is just being a nusiance, like refusing to stand still when being groomed, my friend might shout on make her body language big, but she would never hit or smack for something minor.
For me personally I take a big of a "three strikes and your out" approach. Similar to my friend I'll shout and make myself big the first two times, the third time then I make 'smack' I don't go as all out as my friend, because I'm not training youngsters or trying to assert myself with a new horse, I'm just reinforcing behaviour that they already know and conviently forget
I do try and correct behaviour before it happens though. When I enter a stable, if the horse does not automatically walk back a step, then I will make my body language in such a manner to tell them to walk back, or give a gentle push to ask them to take a step back. It is not punishing, but trying to correct them before the enter my personal space.
When riding I have a different approach. I don't smack with a stick, because my whip is my training aid to ask them to move forward, so I use my voice a "No!" or "ah ah" and then when they get the movment right they get a "goooood" and a scratch. I rarely let anyone record/ watch me when I ride because it goes along the lines of "no! ah ah, good! there! there! goood" ah, no! don't lose it, there! good boy! *high pitched voice* what a good boy! how clever are you! whos gonna be the cleverest olympic pony ever?!?!

" followed by the transition back and lots of pats.
ETA - for me it also depends on the horse. One horse I ride there is no way I ould ever do anything more than a raised voice, because he would just fall to pieces (hes a wimp!) however theres another bolshy horse I help with and I have to be much firmer and make myself very clear as the horse pushes the boundarys as much as possible and isn't at all worried about being shouted at.
Whoops! long post, sorry! As you can tell this is a topic I'm quite enthusiastic about

I love finding out how peoples methods are different to mine