We have a boat house that a nice barn swallow couple has moving into. I don't mind sharing but they poop all over the boat!!! They come every year. Last year they finally nested on a piling under the dock but still roosted over the boat. The dogs just about ate the 2x6 decking on the dock to get to the birds. I have plastic streamers all over, pester them every night, have 2 large labs barking at them and knock there nest down every time. How do you keep them out. So very persistent little birds.

Spring, we have the same problem in the barn but with starlings, and they do their business all over our cars. This is an open barn with exposed structure and trusses, providing lots of nooks and crannies for nests - likely similar to your boat house. We recently sheeted the underside of the roof with some relatively inexpensive 1/4" door skins, and Gary continues to nail sheeting pieces to any remaining exposed cranny. Crossing fingers.

Hope that works.

Well, Gary is taking this as a personal battle - man against bird - so I think if nothing else his persistence will win out. He also shoots (badly) at them with a pellet gun trying to scare them away.