> how do you effectively protect the airspace around airports, powerplants, or other critical infrastructure with such devices?

Use cameras, acoustic sensors, and RF receivers to detect a drone's presence, and use a phased array antenna to shit some appropriate jamming signals in its general direction.

Your local electronic warfare military contractor should be able to set you up with all the equipment you need for such a system.

Airports are not usually places that radio jamming equipment is tolerated.

I've read about training birds of prey to kill drones, seems dangerous for the bird to me though.

I have that drone or a variant, it's very light and small.

instead of sending jamming signals, they could deploy a bunch of "bouncer" drones along the perimeter to knock down the unwanted drones. don't know if its going to be very effective, but at least it will be fun to watch. XD

"The Drone Wars"

Joke aside, is not far from being a real tactic, deploying the so-called "defender" drones, which are guided by a autonomous system, fed by an array of sensors around the perimeter.

I can see myself developing such a system.