I have a drainage ditch/ creek that has water in it 365 days a year and there is a part in the ditch that has eroded away. I want to dig more of the sides away and creat a large swimming area for some ducks and geese. What I dont want is for them to swim away or take off. Will this be an issue? Is there anyway I can make something to keep them in that area? How big does a night house have to be?