I tarp my runs. I free range my chickens. The only problem with tarps AND having a hawk that has been perching In your yard is...the chickens view is obscured they cannot spot the hawk. Trust me the hawk knows where the chickens are. Hawks will test defenses. They are perfectly happy to sit and watch and plan. An experienced hawk will do fly-by’s To see where they run to hide...who’s the slowest...who’s the most unaware. By the time you’ve got a hawk that you can SEE and is comfortable enough to perch atop your coop/run you need to keep your chickens in until you can “harass” him away. Because you’ve got a problem.
With migrating raptors you again need to keep your chickens in until they move on.