I worked with a horse apropriately named Nibbles. She bit me and I popped her in the mouth, shook the lead rope, making her back away from me. Then, I rubbed her face and started practicing disengaging her hind and front end. After about five minutes of working with her, I put my hand to her mouth. She didnt bite me. She hasnt bitten me since then and I've been working with her for almost two years. People think its mean to hit a horse, but in order to be dominant over the horse, you can't take anything from him. Whenever they bite you, make them think its the worst thing they could ever do, even though its not. Kicking and bucking usually come from a lower horse, biting comes from the dominant. When a horse bites you, they are claiming dominance over you. They wont ever really respect you until you brake them of their "habit". Bite him back. He wont bite anymore.