Since you free range yours, I'm not sure how much of this you can do, but this was our solution to our hawk problem. We haven't had any issues with hawks since we did this. We put this in in June 2009, so it's been in action for over a year now.
Our run is our orchard, so naturally the trees are in 2 lines. The day after we lost one of our pullets (laying for 3-4 weeks) to a hawk, I saw it come in for another try. It came down over the coop and flew the line between the trees. Luckily, it was not successful that day.(not to mention me running out like a mad woman screaming my head off at it)
So my husband and I contemplated what to do. Obviously covering the orchard was not an option. We knew that a hawk CAN come straight down, but they CANNOT go straight up (especially with prey) - like an airplane, it needs lift to get out before it smacks into our 7 ft fence on the other side of the run. So our solution was to block the flight path, thinking that if an animal cannot get out, they won't come in to begin with.
We put T-posts about 3 feet apart and staggered them so they were not in a line/pattern. We then attached reflective tape to the T-posts, as I had read that hawks do not like anything metallic, they think it's fire.
It has worked beautifully and I hope we are just as successful in our new run we are building for the new coop.
Here's pics, we call it our hawk obstacle course.
From the coop looking out at the run:
From the opposite side of the run, looking back at the coop.