Do they make such a thing? I think a black sponge like sleeve would be idea. But wouldn't you think someone has made something that will cover the power head preventing anemones from shredding themselves up.
http://ecx.images-amazon.com/images/I/616STq3GhRL._SX522_.jpg
Something like this but thinner and a bigger opening and a cylinder
http://ecx.images-amazon.com/images/I/616STq3GhRL._SX522_.jpg
Something like this but thinner and a bigger opening and a cylinder