Make a 2x2 hidden space where you can place a couple million resources out of site. Similar to tesla coils, the spot would remain unseen until 50% is destroyed. Call the space, buried treasure, with an "X" marks the spot or a treasure chest. If the player waits until it is shown, they only get 10% of the treasure. However, if a troop stumbles over it, before it's revealed they get say 40% of it.
