As long as you have plenty of places for the girls to duck in under to hide, they should be pretty good. Simple stuff just like outdoor furniture, wheelbarrows, dog houses and anything else that would all a chicken to duck in under to hide would be what you need to for them to hide out when a hawk shows up in the local airspace.
Or you could just plant one of the farmers' most difficult pest plants....multiflora roses..... Photos are all from google images.
I like them a lot for protection of my chickens against hawks. A lot of farmers cringe when I tell them that I plant them to provide cover for my chickens. Generally speaking they are difficult to get rid of once you have them.
The thorns are all curved downward toward the base of the plant making it difficult to even brush past them without getting hung up.
This is almost impenetrable by hawks.
Extremely thick brushy plants, with lots of thorns, making it almost impossible to wade through without some type of protective clothing
Good anti-hawk cover for chickens.
Here are some taking over a field.
Goats really like the leaves
We have those growing wild all over out my way. Never thought to dig one up and put it in my chicken pen to keep hawks away.