There are folks that
swear by the fishing line trick, and some people say it has
not worked for them. Every situation is unique, and each hawk is an individual. It may or may not work, it just matters to you how valuable your hens are to you and if you are willing to take that risk! You can get lightweight bird netting pretty inexpensively on
amazon, just search "bird netting" under the Patio, Lawn, and Garden section. If you covered your run with this entirely, it would deter all but the most determined/desperate of hawks. I have read about people who have seen hawks tearing at the netting, but I suspect that might because the hawk got a foot tangled, etc, but be advised that it's possible. Which leads me to...
I have found that hawks sometimes get so focused on prey drive that they don't
see the fine bird nettings. Weaving a few strips of hot pink/orange surveyor's tape (found in the outdoors section of stores, usually with camping and hunting supplies) into the netting seems to help them 'see' it and prevent any crashed, tangled, hawk messes and torn netting!
I have put lightweight galvanized fencing on top of my run, because I also have predators that can climb (raccoons, opposums, grey foxes). Be aware that bird netting sure won't stop a hungry raccoon or oppossum (etc). They would get through it in seconds, which is why I used actual fencing on top. My birds are pets, though, so the loss of a hen would be very devastating to me.