How do you teach or show a dog that biting is bad?

[Kerstyne]

My corgi bit my brother on the back of the leg tonight because he was yelling (and I guess the dog was scared or agressive about this?) and my mom said if it happens again we'll have to give the dog away. Eddy (the dog) has gone after my brother before, when he's yelling or I'm yelling at him, and I know it's not the dogs fault, but mine. He's never broken the skin before tonight. So how can I prevent this from happening again?
Eddy is about 18 months old and my brother is 12.
Also, Eddy has completed basic obedience training (sit, stay, down, rollover, come, drop-it, high-5) and is already crate trained. I know the yelling is bad, but with a 12 year old and a 19 year old (me), yelling is pretty common between the two of us. I realize Eddy is trying to protect me from my brother, and that as a Corgi, he is going to nip. What he did this time was most certainly not nipping; he bit down hard and it seemed to be out of aggression.