Thanks for the information--it's a tough decision. I did the hardware cloth circle when they were tiny, but it seemed much better at keeping the chickens in than predators out. It would not be fun to be attacked by a dog in mid feast, however, so I'll have to think carefully before I bring the babies out again. Maybe it would be safer with two people to handle an attack instead of one?
I know for sure we have coyotes, though you're right that we don't see them. They were a big nuisance where I used to live in Cali, however, and I did golf-club patrol for a neighbor whenever she walked her little dog. The coyotes hung around sometimes and probably would've tried to take the dog if she'd been alone, but they never put up a fight against two people. Eventually everybody started keeping their yards clear of small dogs, cats, and other food sources, and the coyotes went back up the mountain to live a normal life. I don't think the coyotes here have become accustomed to people, so I think my greatest danger is still an untrained domestic dog in a feeding frenzy.
Then again, a guy in Raleigh got attacked by a bear a couple of months ago while he was sitting on his porch eating a sandwich, so maybe there's just no such thing as safety!