Add more explosives-based traps and throwing items-- landmines, bombs, and grenades that do not explode instantly when used... Change their behavior so that they can be set off from a distance by spell damage, other explosions, or possibly even bolts. One good solution would be to give each one its own (very low) before it explodes. Others could be primed with a timer to go off in so many turns. Huzzah! You've added new strategies to the game!