My wife and I have a small garden pond (120 gal) in our backyard that's been there for a few years now. This year it has just been overrun with birds. Not pretty birds, but brown cowbirds and starlings. They crap all over the rocks and in the pond itself. Today I bought two rubber snakes to put on the rocks to try and scare the birds away. I just looked out the window, and they weren't fazed at all by them. Any ideas on what I should try next?