For those who think they are doing their birds a favor by allowing them to free range, you are probably correct to assume they are happy......right up to the moment when the varmint nabs them.....at which point the fun is over. But the one who must be positively giddy in all that is the varmint. He can't believe his good luck.
There seems to be two tracks of thought on this......Option A is to free range and accept losses. Option B is lockup.....and less happy birds.....but still very much alive.
Then there is Option C.....create a set of bubbles or zones of protection. At night, when birds are most vulnerable and predator activity is high, birds are protected inside Fort Knox. This Fort Knox coop does not need to be made of bricks or stone or bars, but is made sturdy and tight. Nothing gets in. It really is not that hard to do. Most who fail at this do so out of ignorance....which is not stupidity. Stupid is not doing what you know you ought to do and assume it won't matter or you simply don't care. Stupid has gotten a lot of birds killed.....but so has ignorance.
Then there is the question of what to do during the day. Wide open, anything goes free ranging is highly risky. So filters have to be employed. These filters are all porous to some degree or another. Dogs, guns, traps, etc, are probably the most porous, but are better than nothing. Fully enclosed runs are the least porous....but are also restrictive. The key is to find a balance of both worlds.
So long term, what has proven to work as daytime filters most of the time are fences. Physical fences are often employed, but these also have problems. Many varmints negotiate these on a daily basis and except for the most restrictive of them, may not even slow varmints down.
What does baffle them and takes the fun out of chickens entirely is an electric fence. The same unsuspecting predator that would crawl under or through a physical fence will try that with an electric fence and get lit up in the process. I saw one of my barn cats get it and he jumped 5 feet in the air and went crazy.....running around in circles out of panic he was going to get it again. Has never been near it since. He has no clue what an electric fence is, only that if he goes near it, it bites. So he avoids it. Long term, predators learn the same thing. They come, they get the crap kicked out of them, they leave. Big time negative reward.
Chickens do the same thing. They learn to leave it alone........so will stay inside. So knowing that, you can enclose an area that is large enough to satisfy the birds (and just as important.....you) with this goal of allowing them access to the great outdoors......where they can chase bugs, eat your garden and do all the things we like to see them do. Only then get to do it in relative safety.
Does this work? I'm going into my 5th year raising birds, and employing the methods outlined above, I have had zero (0) birds lost to predators. That would be none.
. Over the years,I have lost chickens and ducks. I have had fox, raccoons, eagles, hawks and a small weasel/mink. It is so hard to keep free range birds safe. I always feel when they are in their run, fenced in on all sides and top, that I'm somehow doing something wrong. I sell some eggs, neighbors, strangers and some clients. I have a cooler with a coffee can inside. Honor system. Ive never had a problem. Everyone has always told me my eggs are delicious and tasty. This is because I feed them bugs.Even though they are in a large area, have different objects for play/boredom, i want to give them the best “free range” experience. I have cows too. I make different piles of manure for compost. Hay is mixed in. As it breaks down and becomes dirt, there are many bugs!! I scoop up a bunch from each pile every few days and put it in run for my girls and roo. This allows them to scratch and find treats. I also provide sand. They need to take their dust baths. Keeps mites away-mostly. I spray with an essential oil mix too 
Springtime predators are the worst. Everyone is really hungry after winters slim pickings and of course babies. More mouths to feed. I do let girls out sometimes-but only late mornings when im around, and they need to be in way before dark. I have learned this the hard way. More than once 
. I too lost my 4 hens a couple of months back and believe it to be a fox or coyote. All four gone! Just feathers left behind. So heart breaking for sure. It is true, the safest way is not free ranging but they are happier free ranging rather than being locked up even in a big run....I think locking them up before dusk will help. But free ranging will always have risks....I like them happier and free so the risk will always be there.
