The best line of defense against bullying is to become indifferent to bullying. And act like despite the best efforts from the bully, you are just not getting bullied. Or the bully is trying his/her level best and you just don't take them seriously at all. Nothing pisses off bullies as badly as this. You can literally enjoy the expressions on their face when you see how you have defeated them mentally. And know one thing, bullying is mind tactics. And you have to fight it out that way.
Like many innocent looking nerds. I was not only bullied by kids, but by a few teachers too.
Last year, one of my school mates called for re union at a local cafe. Everyone gathered, among them was a guy who helped my Math teacher in high school to bully me. He not only bullied me, but fed the teacher with all sorts of wrong information and got me bullied through him. Anyways the guy was present, and he doesn't seemed to done anything much in life so far. Then my other friends sort of praised as to how far I had gone among all other dudes in our class.
For whatever that brief moment. It looked like the bully's face had dried, gone cold and the expression on his face looked like a greater defeat had been handed over to him.