I don't know of any rooster that can take care of wild dogs. And bantams are out if you have hawk problems. The only protection I can think of that would work is an enclosed chicken run with flight top netting over it to keep predators out. If that doesn't work, electricity does the trick pretty well.
As for friendly roos, my large fowl orpington are very docile with humans and take good care of their girls. I did have an experience with a person's dog got out of their car and went running up to my buff orps who were out free ranging. He was promptly greeted by my two roos I had at the time. I don't think he had ever seen roos that towered over him and I don't think he expected them to charge after him. He quickly turned around and ran back to the car. I doubt most dogs would react this way though, especially large and persistent ones.
