Grumpy, I am guessing the Owl on the boat in Cowes was on a dark red daring on the moorings. It didn't really work, we tried cd's tied to string, tried eveything.
Best I have heard is black binliners tied by two corners so they flap a lot but it disintegrates, perhaps try black hypalon! Also plenty of string to get in the way.
September onwards is always a killer in Cowes, watch the folks with their brushes on weekend mornings - sod farming it in the Galapagos, just move to Cowes and scrape the crap off the decks of the day boats.