I've got some fake rock creation tips. I had to learn this the hard way. One thing's for sure, when you're creating these rock landscapes you want to make sure you "round" the corners of the base of the structure.
If you leave the corners sharp you will have a tendency to accidentally chip off a piece of the sharp corner when putting in the fake rock creation back into it's cage. So "pre-round" your corners and it will be impossible to break them off later!
Another thing I've done is reapply a couple of layers of sealant (in this case Mod Podge) on areas that you happen to notice your pet lizard trying to dig or scratch. I have a pet bearded Dragon that will try to escape, almost on a daily basis, by attempting to dig or tunnel his way through a certain area of his fake rock Mountain.
Building up that area with sealant (WITH OUT sand sprinkled on it) will reinforce it and prevent him from getting traction or getting a "grip" on the grouted landscape.