Unfortunately, one of the biggest problems with having free roaming chickens are hawks. They are sneaky, patient, and fast. I've let my chickens free roam my backyard for almost 5 years before one day, a new hawk comes to the neighborhood, and quickly, within a week, kills 4 out of my six hens. They swoop down, pin the chicken down, and tear it apart. And the only way for this to not happen is prevention, not treatment (like shooting it) because hawks are protected-at least in a neighborhood. I tried putting up those shiny garden streamers in the trees to confuse it, didn't work. Keep them close to people and the house, didn't work. Only let them out when someone is watching them, didn't work. (A dog protecting the flock probably would work but me and my dog weren't there). Now I have two hens left that were too scared to even come out of the coop, so I took them to the farm I am staying at right now. Where they can be in a new place with more chickens, and hopefully forget about their horrible experience.
So if you want your chickens to be free roaming, then it would be good to make sure they have lots of low cover places to hide in quickly. Or put up a lot of netting over where they like to go. And probably only let them out when you are around would be good, too. I've heard guinea fowl are great for scaring off any kind of intruder because they become very noisy and freak out. Whereas chickens usually become quiet when in danger, not guineas, and probably turkeys or geese might make good guard dogs....Otherwise, if you can't get rid of your predator problem, then it would be safest to keep them in a confined area. Or you can let your chickens be free roaming and happiest, but with a very likely chance of getting killed. But even with my hawk experiences, I would still let my chickens free roam. Unless of course the predator refuses to leave, then I'd have to confine them, or take them somewhere else, like I did.

Chickens--aka pig snacks

On the farm I am at right now, we've got a chicken coop next to one of the pig pens (not a good idea in the first place, but space is limited). And one day, Cinnamon the hen decided to go into the pig pen. Luckily I found her in time. She was stuck in a corner just laying there while three young pigs were munching on her side. First of all, animals are so tough. She had a hole around the size of my thumb going in from just above her vent (so lucky) and into her back (so lucky again). The pigs didn't get any organs or any other critical parts of her body. So that was really helpful in her recovery.
Right away I rinse the wound with room temp water and squirt a bunch of iodine on it. Iodine is great for preventing or curing infection. (I've used it on calves and myself too.) It doesn't hurt. Then I pet her in a big box, in the bathroom, which was the warmest place in the house at the time. Just like treating an ill chicken, make sure she is in a clean and dry area, is very warm, in a lighted room, has lots of water, and lots of yummy treats so she will keep her appetite. One of the problems I had was flies, which will lay their eggs in the wound because it's wet and dark, and smells good to them. You can read another person's experience with this at http://shilala.homestead.com/woundcare.html . But we were able to keep them down with the fly swatter and cleaning out her box everyday. Light and keeping the wound dry is crucial. Bacteria (or flies) don't like dryness or light. Every day I would check the wound and every couple days I would squirt it with iodine. I knew the wound was healing because it didn't smell (yes I smelled a chicken's butt, don't laugh :) and it was dry and dark and scabby. I didn't see any white/yellow/green goo, or fresh cuts (like if she was pecking at it, which would mean it's irritating her). And within a few weeks she even started laying again! But I kept her inside until the wound was really hard and was covered by her feathers so the other chickens wouldn't peck at it.
Cinnamon is back to normal now. Except half of her tail feathers grew back straight up, so her tail looks like really bad bed head.
Chickens are fragile, but tough. And if properly taken care of, can heal quickly and become (almost) back to normal. Always ask other experienced poultry people's advice if doing anything risky with your chicken. Each wound is different, and might need a different type of treatment than this.