I like this idea, but the challenge will be building effective ammunition (I suspect depleted uranium might not be the best option here) for frequent engagement, and minimal (read: no) collateral damage.
Thinking about it, shotgun shells should work. Flechette rounds would probably be a good choice.
Thinking about it though, i could get absolutely burried in details rrying to think of counters and counters-to-counters haha.
After reading nogridbag's solution, I'm starting to think golf driving range nets[1] that are used to keep golf balls from flying into the road. You would need to put a top net and probably still have to have an active defense for that one drone to blow the net, the second to run into the plant situation.
It would probably work and be the cheapest solution.