Hi John! I'm new to newts, have one C.O. so far.
I'm pretty sure he climbed it because it was there, lol. And I believe these little guys will climb whatever they find to climb. Hope he's okay!
I have a simple solution for you IF your filter is a hang-on-the-back type- have been doing this on my big frog tanks and it works like a charm.
Get some plastic canvas- you can find it in the craft section at WalMart or at a craft store. It comes in 8 X 11 sheets for about 20 cents a sheet- it's the stuff used for needlepoint work.
Cut the canvas to create a perfect fit (no gaps) around the space where the filter and filter intake tube are. Use electrical tape to tape it snugly to the aquarium hood.
If you have a submersible filter, hmm, good question. There must be some way to prevent the climbing.
~Paula