How to stop accidental shocks from tank heater?

We have had trouble with shorts in the various tank heaters we've used. We only know there's a short when we either see one of the horses go to drink and get shocked, or we notice that they're not drinking. We'll see them standing around the tank, eating snow and looking at the water longingly. By that point they've been shocked, we just didn't see it happen. We've tried the floating kind and the kind that sits on the bottom. Is there any way to wire it so that it somehow shuts off when there is a short or something causing the water to be electrified, so that the poor horses don't get shocked? We would notice the water freezing and know we had a short somewhere without the horses having to suffer.

One really good way to handle these water heaters is to run all of your cables inside PVC piping. This keeps them from getting damaged by the horses or other things in the environment and minimize shorts.

Does your tank have a drain plug? Buy the drain plug kind of heater this way the cord is not inside of the water where it can be damage by the horses or other things. If not, using the pvc and trying to run as much of the cord inside of it is the next best thing to do.