Alternative to egg crate?

[Richer]

Currently I have a piece of eggcrate sitting on top of my overflow. I notched the eggcrate so that it would partially sit inside the overflow. Apparently, the holes in the eggcrate aren't small enough, as I found one of my clowns getting chucked around in there just a few minutes ago. Is there anything else I could try?

-Richer