First off, what is the ambient temperature in the cage, also the temps on the hot and cool side? Second, It is very rare you will hear of anyone using heat rocks anymore. They are overall considered a burn risk to snakes. Under tank heaters, properly installed lamps, panels, heat tape, etc make for safe heating equipment. The rock could be too hot, or to "in the open" (not secure with it being in the open), or the temps may be such that he is at a reasonable temp as is. Add this info and any more that you can and I'm sure you will get some good responses. Best of luck! "Chuck"