How to deter hawks and other birds of prey

We had a huge hawk swoop down in the yard the other day in front of two customers and myself (talking about pigs) and tried to get a chicken. Forutanetly the chickens ran under things and scattered. There is a large fine for killing these animals. Close to $10,000 and jail time. We dont want to because you cant eat them. So i have been on the look out for ideas. One of the chicken groups I belong too suggested mirrors. I am now in the process of buying some up and putting them in my yard. The reflection is supposed to keep them away. Does any one else have any ideas? Mine are all true free range and go in at night into their houses, ontop of stuff in the yard and trees, I have places for them but they go where they like.

We don't have enough space to free range our chickens, besides, there are too many stray dogs and cats in the area. Our pen is completely enclosed, including chicken wire over the top, so we haven't had any problems with predators. Wish I could help.