Thank god I didn't kill him!

[jasonm96]

I know you're not asking me but I thought I'd give you a quick answer and opinion and mine would be either would be fine, though under the tub might be better and be less chance of cracking the glass but only with tub water dishes, not ceramic. The heat might not heat the water much but the frog will still get heated from the bottom glass and tub. Just be sure to put it on a thermostat or you could burn the frog or possibly melt the tub. Tape the probe under the tank on top of the heat mat and then use a digital thermometer that can go into water on top of the heat mat and adjust the temp on the tuermostat to maintain the correct temperature you're trying to achieve