Thorn Shields
I hope that there would be a thorn-shield thingy that can be applied to a building. The thorn-shield would have some hp, and whenever a building is attacked by a melee unit (or any unit NEAR the building), the building would take reduced damage (but the thorn shield takes full damage), while the attacking unit takes some damage too. The thorn-shield would return damage as long as its hp is greater than zero. If its hp becomes zero, then it would be destroyed, and will need to be repurchased again so the player can re-choose which building the thorn-shield will be applied again.
It might be pretty useless against ranged units, but would be nice against Goblins, Hog Riders or Valkyries.
And to balance it, maybe limit the number of thorn-shield that can be used at a time.
