Another thing you can do is make a show of hitting him. Come at him like you're going to take his head off. You don't have to hit him that hard, and you may not even have to hit him...the action is often enough to get the message across. If he pulls up at the action, he knows he's done wrong and knows what's coming if he does it again.
Also remember to come down off the anger immediately. When he responds correctly (Crap, I've done something wrong), pet him with the same hand you threatened him with. It helps him understand that the act wasn't random, there was an action that lead directly to it, and also prevents him from becoming headshy from that hand.
"Sit tall in the saddle, hold your head up high. Keep your eyes fixed where the trail meets the sky. And live like you ain't afraid to die...don't be scared, jut enjoy the ride." - Chris LeDoux