Hey ange,
Check out the "predators" area of this site - on the one hand, it will scare the you-know-what out of you, but on the other hand, you will find that lots of people free-range their chickens under lots of different conditions, and successfully (well, some not) and there is good information there. If you have a fenced area that will keep stray dogs out - and you can and will be out with them - it's probably pretty safe. We have lots of hawks here, but I've never had a problem with them - I have good-sized breeds - but other people have posted that hawks have snatched their chicks or small chickens from right under their noses. So it just depends on your set up, your chickens, your environment, your available guard personnel (you, a good dog, a mean rooster, a donkey?) etc. And luck! It's also good if you've trained your chickens to come to you when you call them, which is pretty easy to do, so that you can put them up into the safe area when you need to leave.