I think the only way to avoid drakes fighting is to only have one drake. My problem is that I really like both my males - Jack and Kitkat - and have enough females for each when I divide the flocks. I would seriously consider not replacing one of them when the time comes. Problem with that is that Muscovy ducks can live up to 20 years and they are only 3 and 4 years old. They might outlive me. Hum - better put a provision in my will for them. 
