Well whatever is put there it has to be patrolled! Heavily patrolled! That’s probably more important then the actual physical barrier. If its not patrolled it ends up as effective as Hadrian’s Wall or the Great Wall.
you can do patrolling easily with drones. It’s a perfect job for them. With GPS technology, trouble locations can be sent instantly to nearest land base.
Cameras in blimps are the ticket
Patrol with drones and cameras
Obama pulled down the cameras that Bush had put up, claiming that they were ineffective because they couldn’t distinguish between animals and man. Seems to me that software could do that now, but even if not, a person looking at the camera feed when an alert is issued could certainly do that.