How do you prevent bullying?

kris
My poor son is destined to be small. Stupid genetics. I'm 5'3" and the hubby is 5'4" and that's tall for his family! He's also mixed race so that might cause some problems for stupid mean kids. How can I raise him to ether prevent bullying or stop it as soon as it starts? I was never bullied that much. My hubby was and it really affected him. How can my son not have issues? We thought about signing him up for martial arts when he's older but would that do much?