Flippers4pups
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I use a double-float system that has a sensor for if the unit sticks on, the second float shuts it off. Between that, and an air gap to prevent siphoning, I have never had a major mishap.
I actually use the very simple setup on autotopoff.com with a simple MJ1200 pump to move the water over. Foolproof for 4+ years, and very inexpensive!
I also use a autotopoff.com double electric float switch. Redundant and has been flawless for 7 years now.