Virtual walls stop virtually no one.
My take is none of these are meant to be used instead of physical walls, they are meant to be used in conjunction with them.
I am also going to guess they can be used autonomously.
I think BeauBo posted an article a while back that showed modular tower units that can be deployed and contain and link to a host of sensors.
I see these drones being deployed autonomously by software alone, being able to fly to a region (perhaps four of them, and they can take up a perimeter in a square moving in unison with each other and keeping the square moving as the target moves, and their sensors linked with each other and with a central location. They can have them parked in a small group near a contested area of fencing with a modular tower controlling them, and all of them data-linked back to humans. Who can put eyes on them and approve missions.