I had an extremely aggressive Cochin rooster. I raised him from a newborn chick. He used to be sweet and turned at about two years old. He nearly killed the bantam hens, would jump on any dog or human, and could only live successfully with LF hens. I tried forcing him to be held, kicking back, ignoring him, standing my ground... Nothing worked. He was still just as mean when he was killed (by a predator; despite all the trouble, I loved him).