Having had considerable problems with guinea on chicken/duck flock aggression, I have to agree with R2Elk here. I don’t know what your specific situation is, and I’m sure that the gamecock owner is correct that some individual roosters could stand up to an individual guinea. However, when my Guineas attacked the chickens or ducks, they didn’t fight fair. The 15 member guinea flock acted as a coordinated unit, like a wolf pack, to separate and overwhelm one animal from the duck or chicken flock. I couldn’t believe that a bird too stupid to fly back OVER the dog fence could coordinate so well in these vicious attacks. I think that Guineas that attack in a group, rather than one on one, are overwhelming. Preventing that mind set seems like the best approach. I had to rehome all but one Guinea male and now supervise (with a stick and water gun) all guinea interactions with the other poultry to prevent my last male from leading a pack attack.