I also would never trust a dog. We had a couple that were supposed to be good guard dogs they killed rabbits and birds chased cows ect . We had to put them down. All of our 200+ chickens free range. My personal opinion on the remedy is guineas. We have 6. They are not the prettiest birds, but they do there job. Most of the time when they set up a racket the chickens totally ignore them. But one time when all the birds were down in the woods( we have a portable hen house) any way I was out gathering eggs one day and I heard the guineas start up in the woods( we have about a 10 acre wood on our 40 acre property we also live about 5 miles from town so there are a lot of predators) All the chickens started to run to the hen house. It was amazing to see all the birds 40 turkeys + chickens 40 ducks +3 geese all come running to the hen house from the woods. Finally the guineas came out of the woods. When they hushed up the birds knew it was safe. Guineas eat very little feed, can be trained to come back to the hen house, plus they can fly and will almost never get caught by a predator unless they are nesting.
I think guineas are perfect.