I had a RIR that started attacking me, and I was able to "fix" him. However, it only worked for me - and he still attacked my husband, brother, and then, when he started attacking the kiddos, he had to go. So...I think, yes, it is possible to establish dominance over a roo and have them back down. However, that dominance does NOT transfer to other people. If a roo starts going after one person, he may continue going after others later...just something to keep in mind.