Originally Posted by
pasta
Seems like a difficult problem to solve; I'm guessing LMG (or any other CIWS) will have pretty limited range, so you need one deployed near every target. To defend an area you need some sort of guided missile, which quickly gets complex and expensive (I'm guessing more expensive than the drones you're targetting). The only other countermeasures I can think of are electronic (deny control of the drone, or its ability to navigate) or some sort of directed energy (shoot them down with lasers).
I thought that birds of prey had been used; cheap to manufacture.