When I try to hit the Digger with Sponge gun, the Digger senses the Sponge and starts walking towards it. Not giving enough space in between to hit him towards the mound.
When you have a Sponge Gun, you are at a different level from the digger, so hr should not be moving toward you at all. Shoot him TOWARD a Mound (perhaps more than once) and he will move to dig up the Mound. Then he will sense another Mound, and move to dig it up as well.