My parents had a problem with seaguls pooping all over their floating raft, well not so much the
poop, but the fish bones that would be left and stepped on. My dad got a windsock/sail and hooked to a piece of conduit as a pole from the edge of the raft. The windsock looked like an eagle and worked really well, no seaguls the first year. In the spring of the 2nd year the string broke and the windsock was lost, the seaguls quickly reclaimed the spot. My dad went out and got another one, but this one was some crazy multi colored twisty thing, he replaced the string with some light chain and some fishing tackles and it's on about it's 4th year now. I would say it keeps the seagulls away 90% of the time or better. There seems to be one bird who isn't scared of the wind sock, but does seem to be scared of the
BB gun for some reason. Not that my dad or I would ever shoot at a seagul, that's illegal here afterall, but shooting right next to it or as I like to say, "firing a warning shot off his bow" seems to work.