The easiest way to fight George is not to fight him. Shooting him, blowing him up, and even knifing him will cause him to roar in fury, then charge at full sprint after you and your allies until everyone is dead. If this occurs, you can lead him to any large body of water to calm him down. Until you obtain the new wonder weapon and upgrade it via pack-a-punch, you will not be able to kill him. Also, the power must be active before you can damage him.