The fishing line (unless fly line) probably wont deter the hawk from making the attempt but will get them right tangled when they do.We strung fishing line above part of the breeding coop run ... now a grow-out coop & run for about 1/3 of our chicks ... to dissuade the hawks. It doesn't photograph well, fingers crossed it works. And there is still a big part of the run left to do.
Meanwhile, I heard a commotion in the free-range flock and saw dark flapping wings in a wooded area. I ran out there, down to the fence line, and found one of my good Delaware hens on the wrong side of the fence surrounded by a mess of her own feathers. I think a hawk had picked her up but couldn't manage to carry her very far. Not dead, no blood. Just scared quiet like they get.
Hawks are NASTY this year.
Ive read people use colored yarn or string so the hawks think they cant get in.
Clear fishing line will probably get you chickens too if they try to take off over the fence