We also have most every predator known to chickens here (raccoon, coyote, other dogs, feral cats, hawk, owl, weasel, fox, very occasionally a cougar, etc.) and have not lost a chicken while free ranging... yet. I have only been free ranging for a year though so time will tell.
My dogs are always out, now, with my chickens and/or I keep a very close eye on them. I also have larger livestock milling around (horses, llamas and goats) so I think that helps keep some of the predators away also.