You might not be able to bury the heater. Some heaters can't touch gravel or don't work when placed at the wrong angle. Check the instructions manual the heater came with or search online before doing that.
I sympathise with your situation, though, because my boy managed to burn a huge chunk off of his forehead a month back. It looked truly awful, but I just put a teaspoon of aquarium salt, and began to see signs of healing by the next morning. Now, it's impossible to see that he ever had a run-in with the heater in the first place.