@PirateGirl ... Try the terracotta pot thing.... I'll try to post pics (we've taken ours apart for next winter already). Basically you put a couple pavers down, use a "naked" heat lamp (no dome), upside down the pot over the lamp, put the plate to it on top, then set the water pail. It doesn't melt the pail but puts off enough heat to keep it flowing into the reservoir, also the pot it's setting over puts off heat to keep the chickens warm in the cold. Got the idea, surprisingly, from Pinterest. works decent..
I have seen this and have a few different light fixtures that would work. I may give it a go next year. The ducks play in their water so much there's usually a hole on the ice (or they break a hole in the ice).