We have our bird scarer at our dam. We have a dock that used to be covered in duck poo but since the scarer, has eliminated 99% of it. It's wasn't an over night venture, it took a few weeks for the ducks to simply get annoyed at the sound of the bird distress calls. As for our floating trampoline just 10m away from the dock, it still gets poo on it, but a slightly reduced amount.
Environmentally friendly, good features like volume control and timer.