Amazing Goby Disappearing Act - He's Alive!!!!

[Delphinus]

Actually it just seals the top of the overflow so it's above water. It's basically there to stop any potential jumpers from jumping into the overflow. My overflow teeth are small enough to stop most things (Catalina gobies maybe would fit, but then, I don't keep any of those). It just sits on top.

I think you could do the same for the top.

As for the teeth though. I don't remember how your overflow looks, is it teeth though plastic or is it glass and thus a piece of eggcrate? If the teeth are eggcrate I wonder if you could get away with doubling up on it. Unfortunately window screening is pretty fine mesh so I think it would totally clog in no time if any of it were submerged (or had water running through it). But doubling up eggcrate might be enough to prevent a fish from swimming through it...