I use to use the heavy rubber horse feed pans for water in the winter. You can stomp on them to break up the ice and they are fine. I made a cover with 12" X 12" plywood set on 6 1/4" legs. It works OK, a lot of stomping though. WELL, I just found a better way. We buy mushrooms in small plastic tubs, they are about 4" x 5" and Very smooth inside. I used silicone and glued 2 together ( so they are not so twisty, can pick them up better ), anyway all I have to do now is press on the bottom with my thumb and the ice just pops out ! In the lofts with more birds I can set 2 under the cover.
Good thing, they are free and if they break - Well, we eat lots of mushrooms !
WORKS GREAT !