Stully - you've got it.
Great Pyrenees are a good guard/family dog too. Check 'em out here
http://www.akc.org/breeds/great_pyrenees/ These dogs are to be raised with livestock, sleep with them and such. I don't know how you might work that out with chickens.... but they only bark when doing their job. The livestock keeps them company/family and gives them their purpose. Dogs with a purpose don't do the usual irritating dog things. But we are talking about 'working' dogs here and not house pets.
If you don't get one of these special breeds and/or cannot raise it with livestock I would suggest you get two dogs. Giving your outside guard dog a 'pack' helps the needless barking to an extent, and of course training to give them a specific job helps too.
One more thing - even though these special guard dogs will cost more than an animal shelter dog - when raised with livestock you don't have to do much training yourself. For some people this fact alone is worth their price. Proper training of working dogs can take a lot of time and work, so matching the dog breed to the need is well worth it IMO.