I use ceramic tiles.
Most of my tanks are the fancy terrariums with sliding screen tops. They come with a hole in the botton for i guess a heat rock cord etc. So i have put some *sticky* tile over the hole and on about 2/3 the glass so the ceramic tile doesn't scratch (one tank is badly scratched all along the bottom edge of the sides
) The part left with just ceramic tile is where i attach the UTH. Once the gecko has decided where the bathroom is i put a few layers of papertowel.
My crested gecko tank has nothing on the bottom as its easier to clean for me instead of taking him out everytime he poops so i could change the papertowels.
Red 
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1.0 crested gecko
1.0 leopard gecko
(hoping to get 1.0 blizzard, 0.2 patternless) 
1.0 papillion (small dog)
2.0 bettas
and 2 very annoying younger brothers LOL