K, I have an idea and wanted your input please? I have a shelf on the one corner that could prolly hold either a small preform or maybe on of those small pans like you mix cement in. My thought is something like that with pea gravel in it, to put the dwarf cattails, and some other plants in for water filtration? I could nestle some potted plants in it, too. This would be under the water so the fish can swim thru it, and hopefully be fine when the pond freezes over? I keep on end open in the winter, but this corner will freeze over? I'm thinking this to keep the gravel confined to one area