My ducks will bully the chickens, so I prevent it by keeping them apart during the day. At night they share a 12'X20' barn, but the chickens roost up in the rafters and the ducks and my gander have a big stall with shavings for bedding. In the morning, the waterfowl go up a ramp from their stall to the outside covered chicken run, through the run gate into their own big waterfowl pen, and the chickens come down from the rafters -- they always wait till the waterfowl have gone outside -- and have the run of the barn and chicken run.
The waterfowl go out every day except in really bad weather. When everyone has to share the barn (and covered run), the waterfowl dominate the stall and run, and the chickens make do with the barn aisles, shelves and rafters. It works out because there is enough space outside the stall so the chickens have room to move around and get their own food and water. Fortunately, it's rare that they all have to spend days cooped together.