My dogs are in a fenced back yard approximately 30' from the chicken pens. They do not free range outside of the fence. (They do however come in the house once I get home from work.)
The chickens free range only when I am home. When I am gone they have netting covered runs to frolic in. When I am here they have approximately an acre to range on. I do not for a minute believe the netting will stop a determined predator. It MIGHT slow them down.
That being said, I know my dogs are a predator deterrant. One of mine is very visual and she can see a hawk before any of the rest of us. She often alerts the roosters to danger. I have heard her do her "bad, scary thing" bark and then the roosters all give the danger call. Conversely, when they do the danger call before her she starts looking around to see what is wrong. Clearly they understand each other to a certain extent. The lone hawk that made a low flying dive (while I was out there anyway) was chased down the fence line and into the trees. I never saw it again.
Dog #2 (in my avatar) is ground oriented. She can smell trouble coming. I'm convinced that the only reason I have had zero ground predator problems is that she watches the coops and barks like a fiend when something comes near. Plus, my yard smells like dog and that has to help. They shed like crazy and I drop handfuls of dog fur around the pens. If they were boy dogs you better believe I would be out there having them pee on the coops.
Now, do I think my dogs make me predator proof? Not on your life. I think they help, but it is still my responsibility to be vigilant. The next big coop project is to cover the tops with chicken wire and replace the netting. I daily walk the perimeters to check for signs of digging. I only range when I can be around to supervise. The dogs will only help so much.
I do think that the hawks are aware of the dogs and tend to avoid coming near if there is a better food option. Thankfully there is a HUGE field behind my house and the rabbit population is insane. That meal is a lot safer than dealing with the dogs.