Man, I don't think you've ever actually built free optical laser networks, they are kind of a pain in the ass and everyone is going to notice you've got one stuck up on a pole.

The next time its foggy or raining a tuned photon sensor to the spectrum that these devices run at will light up like a Christmas tree. If you're really intent on catching said people, you'd have drones flying around sprinkling light chaff and detecting where it detects optical scattering.