I agree with whats been said about charging them at the fist sign of aggresion and not letting them dance or display in your presence and being consistent , All excellent advise.
Where I have questions is about not letting them crow or mate in your presence.
I have 3 1 1/2 yo roo's, We worked out the fact that I'm the Alpha when they were about 8 months old at the first sign of aggresion. I followed the above guideline with the exception of discouraging mating & crowing in my presence and have had no issues at all with reguard to aggresive behavior.
I can turn my back on them, I can pickup even the most skittish hen while it screams bloody murder, and the roo's make no attempt to intervene, they don't run over to me or anything.
They're not all docile breeds either. One is a big Rhode Island Red, and they are notorious for being nasty, ill tempered roo's.
These roo's are very fierce defenders (one killed an unlucky crow that had the gall to land in the run), so its not like they have no will to be aggresive, just no longer toward humans.
It would seem that letting them crow and mate in my presence has no bearing maintaining my position as Alpha.
I would have a hard time believing that my 3 were just exceptions to the rule, and it can't just be in how they were raised as chics because 2 of them were raised elsewhere and I didn't get them until after they were mature.