Some roosters simply will not share their hens, period. My 6 year old Delaware is one. He is fine with his sons until they start flirting with the hens. He actually killed a gorgeous 20-something week old cockerel I was planning to breed, one who was larger that he was, and almost killed another he had been living with semi-peacefully for a longer period. I had to remove that one after he was injured seriously and he now lives in a different coop with his own few hens.
That Delaware rooster's son, Rex, was also taken out by a lucky hit with his brother, Deacon, (coincidentally, Deacon is the one their sire hurt badly) who finally had enough of being chased away and turned to fight, surprising his brother and causing internal injuries that led to his demise. So, I guess it's in their genes from dear old dad not to be amenable to sharing their hens. I would never, ever put a strange rooster in with any rooster here, no matter if folks tell you about introduction periods where there is a fence between, etc. Someone would most definitely die.That fence only makes them more revved up to get at each other when the fence is gone. Mine fight at the fence constantly and when the barrier is gone, they are like dogs who've had sticks poked at them through that fence and are ready to bite.
This is the general nature of roosters, to protect the hens and their bloodline. There may be exceptions but you won't know if you have one of those or not until there is a dead rooster on the ground. You are more likely to be successful if a youngster is raised up in the flock with his sire, though. But, then, you have to start watching the situation closely so you don't have what happens with my Delaware every time (the guy in my avatar)
