There is this pigeon couple which time and again try to build their nest on my apartment balcony. If I'm at home and see them approaching, I will shoo them away. Yet they are still not giving up. Their poops are all over my balcony and are so smelly and they often mess up my balcony with little twigs. This morning I found a white egg, presumably theirs, on my balcony. I swept it along with a bunch of twigs up and bin them away. Is there a way or ways to prevent this couple from coming back?