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.

It seems relatively simple to me to detect fibers hanging around cities as soon as the network is bigger than two nerdy neighbors. Same for lasers and telescopes.

ud need tons of beams tho do maybe its easy enough to segment the network badly by finding bunches of them?