Bog Rim for Pond Planter

I have never really liked any of the nursery containers that things like water lilies grow in, but like even less the kinds of pots that need to rest on the bottom of my pond. This sketch is my compromise: make a ceramic rim that slips into the top of a 3-gallon container with a flange that can retain additional pebbles (to hold the soil and keep the fish at bay) as well as providing some additional cover (under the rim) for the fish to hide.

This project is actually happening...I hope to have finished images up soon.