Sure, take some gutter guard and attach it to the top of your overflow, to prevent the anemone from going into the overflow, kinda like adding a fence to your overflow.
I added some to mine, b/c there was a small gap between the return line and the side of the overflow, enough of a gap for a small, unlucky fish to make his way into my overflow. Just zip-tied it in place using the teeth of the overflow.
If you can't find black gutter guard anywhere, let me know, b/c I have alot of extra lying around.