I've never had one fail yet, mine are hooked up to a low pressure system so I don't have to refill a bucket. I only have one per cage and I have 6 or 7 birds in each cage.
I've never had any problems with predators but my cages are raised and also inside a fenced area with chicken wire on top. You could mount them on the inside if you don't want to cut a hole in your cages.