Yeah, we started with egg crate up there to block the overflow, but the more determined (and smaller) fish kept managing to sneak through. I pulled out the egg crate and sewed on gutter guard (smaller grid squares than the egg crate), offsetting the squares so that the openings were then even smaller. Just sewed it by looping fishing line through all the way around. Now we have two pieces that fit on the overflow and we can pull them out to clean them if we need to once in a great while. Effective!