I don't know if it would work on raptors but many of our local berry farmers have discouraged birds by tying long strips of mylar to the bushes. Perhaps doing this to the perching areas over the pond would work. I do think that they would eventually adopt and ignore it but by then the screamer gun might work again for a while. One local grower of landscape shrubs was able to stop killing deer some years ago by rotating several methods of non-lethal tactics to keep the herd from becoming accustomed to any one of them.
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all leaders tangle; mine are just better at it than most. Jim
I can think of few acts more selfish than refusing a vaccination.