Add a warning system similar to Dwarf Fortress to help prevent players from digging into adjacent lava, water or empty spaces :
While wielding a pick axe, check blocks neighboring the block the player is aiming at and prefix the block name in the UI with 'warm' in case of adjacent lava, 'wet' in case of adjacent water and change the sound of the pick axe striking the block if there is an empty space not visible to the player behind the targeted block. This should only work with stone type blocks or any 'hard' blocks placed by the player.
Thank you for your consideration,
-mgfx