We rescued a "bad" dog from death row through the help of a St. Bernard rescue. (I needed to add/edit that she is more than 1/2 Great Pier, but has the markings of a St. Bernard.)
She came with GIANT suitcases full of baggage due to her past. It has been a very rough road for us all. We almost gave up on her too because she acted like she hated us and only wanted to run away, was aggressive toward other animals and very unruley towards people. She drug us down onto the ground countless times. The worst dog in the world!! (At least Marley was loveable, Kate acted like we were the enemy.) I am only saying all of this because it will prove almost any dog can turn itself around, with time and dedication.
She is now the best dog in the world...10 months later. (She finally loves us back!) She guards our yard (and chickens) 24/7. Now she can even behave with the chickens out side of their run. The simple trick when it comes to our chickens, (and this is only for extreme cases, like Kate) that we used was a (child's)sling shot and one rock. It was either that or back to the pound, we tried everything else! We were so desperate, we even bought a shock collar, but it didn't shock right when you pushed the button, so it was cruel AND worthless.
Of course we have constantly been working with her on her "ground manners" and gave her unconditinal love etc. But when it came to the chickens, we needed something that would get her attention from a distance. I am sure if she got to the chickens, she would have killed them all. I only hit her once, that was all it took. When she needed a tune up, I only pulled the rubber bands back and let them go, no rock. The sound it made was all that it took to redirect her. Now, she is perfect. It took about one month of direct supervision. We said NO first before we made a move with the sling shot noise. Then just NO worked and now she doesn't bother them at all.
It worked. But I only recommend this for extreme cases. Hope this helps someone.