i just had an "Aha!" moment. I have some velcro strips in a box with some art supplies, and they have a sticky back to them. I think this might be a good solution. This will make for easy removal and if i have to replace it in the future i'll just slap some velcro on the new one!

I did notice this morning that my hygrometer had a water build up inside, making it very difficult to read. Perhaps this contributed to the glue going bad? It may just be that these things only last a year or so, I'll see if i can still salvage it.

Let me know how that digital therm/hygro works out, and if it does, what the brand name is. I don't have a wally world anywhere in my area but stores may carry the same item.