The birds have been getting worse and worse at my mooring spot, leaving several really stubborn messes on my roof and canvas every day. Just this last Saturday I put together a PVC contraption that settles into the space between the hand rails and raised roof, with a 45 degree cantilevered section extending out over the flat section of the canvas. (I have a bimini type awning that goes about a third of the way back, with a mooring cover sloping from there to the stern. They really like roosting on the awning.) I put short verticals at each juncture and enough cross pieces to stabilize it. Then went all the way around the verticals with some fine stainless wire, crisscrossing with X's for good measure. It's not too elegant, but it actually isn't much of an eyesore when it's in place. It's light, and easy to lift on and off, and since my (friend's) dock gets hardly any foot traffic, leaving it on the dock while I'm out isn't an issue.
And the good news - it's been five days and NO MORE BIRDS! (knock on wood).