It has been my experience that roosters won't fight (much, if at all) if there are no ladies. I keep my cockerels in a grow out pen, beside the coop/run that houses my laying flock with their attendant roo. The cockerels do a bit of "establish pecking order" fighting, but do not do any "out to kill" fighting. I've kept 2 roos in the laying flock, and they generally get along UNTIL the younger one decides that HE wants to be the Alpha. I have almost always been able to cull the older roo before their relationship gets to the point of bloodshed. Of course, a lot depends on genetics. Some breeds are more aggressive than others. And, a lot depends on how they are housed: do they have plenty of space in coop and run, do they have plenty of options for "getting out of each other's sight". Of course, best option (which I am not able to provide) is free range.