The trick with holding them down is to do it till they'll stay down even when you let go. I've done that to mine and he is a very sweet boy. He still sort of tries to be dominant from time to time but only in ways such as not moving when I walk toward him. He gets bowled over as I walk right through him and that's the end of it.
But only after I held him down until he stayed there without moving so much as a feather after I let go. I let go very slowly, and if he started to move, down he'd go again. Finally they'll stay there till you TELL them it's ok or walk away. He never did get super mean, I never let him get to that level. I correct their butts at the first sign of aggression and so far no problems. But I've only raised three roosters so far, so maybe it doesn't always work.
In any event, good luck with him.
Someone on here told a wonderful and hilarious story of a kid with a favorite rooster that attacked her. The girl finally had had enough and came stalking into the house, grabbed a dishpan, put dish soap in it, then went out and proceeded to give the boy a bubble bath in front of his hens, telling him the whole time things like "Shut it! You do this again and it's the blowdry treatment too!" The story is just hilarious and more... it worked! I really have to find that and bookmark it.