Where should I put the thermostate probe and why?

[PitOnTheProwl]

Even if the water bowl spills, which has never happened, the temps would only spike for a short time - and even then they would barely spike. I poured water from my fridge onto the setup to test this at the beginning and it spiked from 90 to 98 for about 10 minutes at 100%, and then it started to drop again. No harm.

I have often wondered how "water proof" they are. Either way I wouldn't gamble on it. Just my thought.