you can certainly train a bad (aggressive toward you/dd) roo to be better, you have to make him know that you and DD are boss. I would carry a broom with you, and if he comes at you, swat him (don't hurt him) with it, for a few times, don't turn your back on him, and maintain eye contact. Eye contact among animals is one of the biggest alpha/submissive tells there is. After a few times being swatted with that broom, he's not going to want to attack you, and he'll know you are boss, you have to be head roo, or he'll walk all over you.
I had to re-train my alpha pullet after we re-homed our young roo, because she was pecking and being really hard on the other 5 girls, especially the new one, who remains on the bottom of the totem pole. I'm the boss of that flock, and alpha girl knows she's second in command now, and there is hardly any pecking from anyone. She would chase the other girls around whenever there was a treat, she would growl and not let the lower girls get anything, so I started chasing her around, just her.. Worked like a charm.
If you want to keep your roo, do some research, there are lots of threads on byc about alpha/aggressiveness and re-training.