I have one ahhh in a drawer someplace under a broken keyboard.

There are two schools of thought on probes some say on the heat source and some place them inside the enclosure.

In either case the probe MUST not move. Inside offers higher accuracy but more opportunity for movement as the snake might be able to dislodge it. Out side placement I use electrical tape on the UTH I place mine on the back of it so the pad heats more evenly.

interior placement I use hot melt glue over the probe and along the cord. If you are using a glass tank I'd leave the pad on for a while so the glass is warm before gluing the probe down you will get a better joint.

The probe must not move. This cannot be said too strongly. It doesn't matter if the snake moves it or the cat either is a potential life threatening even for the occupants.