Hey,
I did a fake rock wall a while ago and posted some stuff on the forum about it. I used some different materials, but maybe it will help you get some ideas. It has held up this entire time and the lizards have been pretty happy with it. This rock wall has kept their claws at a good length and they use all sides of it.
Here are some pics: forums.kingsnake.com/view.php?id=1461419,1461419
Here is the material list: forums.kingsnake.com/view.php?id=1461419,1461639

Hopefully this helps some. Good luck! It is a rewarding project when the time is taken to do something like this for your lizard pals.

- Matt
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0.0.3 Desert Iguanas(Dipsosaurus dorsalis)
1.1.0 Tucson Banded Geckos(Coleonyx variegatus bogerti)
1.0.0 California Alligator Lizards(Elgaria multicarinata multicarinata)
0.0.2 Pacific Tree Frog(Hyla regilla)