I think a nice packed clay heavy dirt could work. Pretty? No. But that essentially what they live around in the wild. Staying away from the sandy areas and living within the rocks/dirt grassy lands. And yes, geckos lick a lot. Everywhere they go. That excavator clay may be more what you are looking for as I think it has a red hue. Not sure how it dries etc though. Trying to find the thread that had a picture of some hatchlings in a bucket of compacted dry dirt. I remember thinking they looked right at home. I'll try to locate it.
Thank you, that would be great!
In all honesty, I thought that stuff was called sand. Had I known it was clay, the thread title would have been a lot different.