I use this IR gun, so far it has worked great.

http://www.amazon.com/gp/product/B00...ls_o03_s00_i00

You typed hydrometer but I think you are asking about your Hydrofarm Tstat probe. It sounds like it is located in the right spot. Like others have stated the differences in uth is great. Depending on yours I would be worried that the glue might melt and make a mess or ruin your probe. The substrate should anchor your probe fine. If you want an anchor you could get a fake silk plant from any pet store to hang from your tank wall to house the wire and give it some support. They just use a suction cup to stick to the side and stand up well to critters. They also hold water after misting helping your humidity and give your snake a place to drink from. Mine will often drink from the leaves in the tank.

just remember that the thickness, type, moistness or dryness of your substrate will make your surface temp higher or lower than what the uth is set at. Thats where the temp gun comes into play to get it right.

Tip: for more support of the wire you could use zip ties to anchor the wire all the way down the plant branch. I would use a lighter to soften (round off the sharp points) the edges after you snip of the tails. Just kiss the sharp corners with a lighter and rub them with your fingers. I bet the edges wouldn't hurt your snake, but better safe than sorry. This may be overdone, my snakes don't pay my wires any attention.

DO NOT USE TAPE WITHIN YOUR TANK.