To help make sure the Chem does not eat the dirt. you can buy some river rocks (The polished ones that are oval shape) and place them over the dirt. I do this in all my cages. Make sure the Rocks are big enough that the Cham cannot eat those.
I get mine from Michaels art store. I believe you can buy a big bag at Home depot or Lowes. They are called Mexican ??? something or another. they are in the garden section.