I've had this same problem. At first I was concerned with trying to change the birds behavior. It never worked. Well, to be honest, it worked great so long as they knew I was around. They would just wait until I was gone and then take the violence up a notch. I came back to dead hens and chicks once too often. Forced submission on a rooster will teach it to respect the person dominating it, or at best all people. There is no way you are going to rewrite their programming to the extent that all your hens will be safe.
My new regimen is to incapacitate them by hobbling until the other birds have all dominated them. That really doesn't seem to take long once the others realise that one of their own is weak, does it? If they get back to seriously wounding or killing the others, and I include denial of food, water or peace as serious, they get eaten. Check my early posts, my poor girls were getting scalped frequently. I don't think roosters are necessary here, and they are certainly plentiful if I should need a new one. I'm still waiting on a "nugget" class rooster, though.
