If you will add peat moss to your play sand you will find it holds tunnels better. I used to use that years ago. Then I tried digging dirt up out of the back yard and found the chameleons and other lizards responded much better to it- probably the smell and texture. Really, not many lizards lay eggs on the beach. Another trick I use is to cover the surface of the substrate with dried leaves to give the lizard a feeling of cover and I'll put a flat rock or piece of wood on the surface near the wall and start a tunnel under it so there is a solid roof over it- usually the chameleon will start digging there. Some of them like to start where I place dried roots or branches pressed into the earth.
