Instead of staying in my 120 year old barn, the swallows have been nesting atop my several light fixtures on my covered house porches for the last 30 years. I need a way to prevent their nest building other than my removing the beginnings of their (mostly mud) nests every few days. The mud on the porch floor comes first and later the droppings from the babies. Although they are fun to watch, I can see them any time I want down in the barn where I don't have to clean up after them. Ideas???