I actually work in the drone detection/jamming field. My only surprise is that this sort of thing doesn't happen more often. We already see drones used for drug smuggling and privacy violations, as well as the use of drones to carry IED payloads. Drones are an amazing tool but as with any tool, they can be used in nefarious ways.
I presume the cheapest protection would be fine netting. Is there any indication of netting being used as protection against drones? Or would netting be to obvious that there was a target worth targeting?
drones open the door to all sorts of malfeasance that used to require state level backing to accomplish and counters are only coming into play if not concept