Mine free range all day too. We hardly ever see hawks and when we do they don't stick around for long. They would have plenty of the sky rats to prey on before any of the chickens around here. We also currently lock them in the coop at night but it's more to control the rooster's vocals at the break of dawn. As soon as he's gone they are free to come and go as they please.
Mine are out all day too. I haven't seen any hawks but I did have a coyote jump into the back yard over the block wall. He fell in the pool and then I chased him off and I haven't seen him again.
I guess he figured there are easier meals elsewhere.
4 Ideal 236 leghorns, 2 BA, 2 PR + 2 EEs
(RIP Arianna, Phoebe, Ursula, Estelle, Eva, Peach, Ruby, What's her face, and Opal)
**Funny chicken video by my daughter** http://www.youtube.com/watch?v=qV-FYmQ5Fio