Whenever I moved, I had no problem becoming popular quickly. My aggressive, red-haired, younger sister would warn people, "Don't mess with me, my brother will beat you up!"
I had to learn to fight. At every new school, I had to beat up the bully. Teach your son to fight. Send him to martial arts training. After I learned to fight, I never fought again.
People who fight, fight because they fear. Most of them come from abuse, usually both physical and verbal. The best lesson on fighting I ever learned was this:
Agree to the fight, one on one, in a place no one from school will be. Once on site, tell the other person, "Listen, at school, I was not interested in fighting. However, in front of everyone else, it is difficult to back out or make an offer of peace. I thought you might feel the same, and that we could have peace between us." That only failed to work just once.
Composure is important. Bullies are fearful, and cowards. They will avoid anyone who looks strongly individuated. Look people in the eye. Walk normal- muggers go after people that are "off" somehow. Funny walks and frumpy clothes signal a weak, beat-down personality, an easy target. Same for those who look down.
Also, be sure to pray for bullies and send them love. Hate requires a two-way bridge. If only love is going out, the enemy cannot attack.