I agree that gender is not the issue. My first horse had a serious biting issue, which after 3 years (and him finally understanding it wasn't okay), left me with several scars on my arms, a messed up shoulderblade, and a huge respect and understanding of the horse's mouth and how to prevent biting. He probably started out innocently enough, and then as he got worse and worse, the previous owner decided to start punching him in the soft part of his nose. This to him just became another game to play, so he would shark you, and then jump back to avoid the fist. I was appalled when I got him, and the girl said to punch him in the nose. With him, because the face was now a game, I had to resort to basically ignoring him, and as soon as he started to try and bite, I'd smack him in the chest, and then continue on as if nothing had happened. It took three years before I could trust him enough to even turn to walk away. I agree that the lip or nostril pinching will work, and is a good idea to start out with, as long as he hasn't gotten to the point where he thinks that its a game to bite and dodge the fist. Otherwise, I'd smack him in the chest, just like a herd mate kicking him when he bites their butts. Biting is a serious issue, and I wouldn't take it at all lightly.