My neighbor has three heelers (not sure which kind). She's worked extensively with them and her flock to get them to not mess with her chickens. Unfortunately, most of our chickens were killed recently by a predator (couldn't have been by her dogs, but for the sake of brevity, I won't explain unless asked). Until she fixes her run, she's been leaving her heelers to guard her chickens and things have gone really well- no more predators, no more chicken deaths.
I personally wouldn't be comfortable leaving my chickens alone with a dog, but I've seen it work out well.