I haven't read any responses yet, but I've dealt with more than a few horses like this. I find hitting them is usually just asking for a fight. In fact I have a pony that the more you hit him the more violent he becomes - even one trainer who hit him until he was backed, crouched into a corner licking and chewing in submission - as soon as the trainer turned to leave the pony had two hooves and teeth on him before he could take a deep breath. Luckily there were a number of people around.
My solution for this pony was this:
First off, I needed to make it horribly uncomfortable for him to have his mouth anywhere near me. So while he was standing being fine, but I could see in his eyes he's thinking about being naughty I grab his nose and rub hard on each nostril, just rub him up and down really fast. He usually just backs up and tosses his head up - that's a GOOD response, he got out of my space. Of course that doesn't stop him from coming back. If he actually a bite, I grab and pinch a chunk of skin, usually on the side of his neck and I squeal, high pitch and loud! This is the equivalent of another horse biting him back and squealing harder. Of course if this horse is at liberty in an open field that would NOT be a good option, as he could easily swing around and kick you. Even a horse submitting to another horse may run away and toss a defiant little kick. So only attempt this if he's well under control, in a stall with you on the other side of the door, or on a lead under control, or tied. Do Not EVER pull an ear! Ears and eyes are off limits, I assume you know that but I'm putting that in there for any random someone on the internet who may read what I wrote as meaning you should twist their ears off.
Then, after squealing and biting him back, that's good you made your point, biting is bad. But now you need to teach him not only was he bad but you are in charge.
Now I would reinforce all of his ground work, fast and furious. Making him back up, making him yield his hind end, front end, side pass. Make him dance until he's submitting. Any act of aggression should be met with more work, any attempts at biting should be met with a bigger 'bite'.
I don't find using tools to work well, even whips, they make the point, but they make the point that you're defenseless without the tool.