I do not have a HUGE hawk problem, but live in an urban area where I see hawks circling overhead daily; at least during the summer. I have had a few times found a hawk perched nearby watching my hens. Fortunately the hens have plenty of hiding spaces under shrubs in the garden. I would see a hawk circling high then seems like they would come in for a closer look.
Due to the heat in the summer I string up triangular shade sails, which provide some visual barrier to raptors. But in the winter I need to let the sun in for the garden. After taking down the sails the yard felt pretty exposed.
Similar to an earlier post, I did some research and decided to string twine from fence to fence and from house to fence, making a web of flight-path deterrents. The key to making it effective to to make the mesh 3D; varying the heights of the strings rather than making it like a thin net and running the strings at random angles.
The raptors eyesight and depth perception is exceptional so as noted earlier they won't attack unless they have a predetermined escape path. Either that or they are just really bold.
I used about 3000 feet of sisal twine to cover my 30x60 backyard. Cost under $10. I still see the hawks circling high, but since putting up the mesh haven't had a single incidence of someone coming for a closer look, despite the lack of shade sails.
Either that or it's just a seasonal thing. Maybe they will be back in the spring... ??