I have 2 very large GSDs-5 and 8 yrs old and a 26 lb rat terrier-2 yrs old. None of these dogs had ever seen a chicken before I got mine 5 months ago. My oldest GSD has HUGE prey drive and was my biggest concern, but I also have spent a lot of time training my dogs. It took consistent supervised exposure, but often now when I go out to feed my horses, the dogs AND the chickens all come supervise ME! There are times when I take the dogs for a walk and I have 3 dogs, 3 horses and 5 chickens all following me. It's quite the parade! My 5 yr old GSD LOVES the chickens and the horses. His father was a "chicken herder"
and this dog is completely safe around them.
My birds free range during the day and I have a 1/3 acre dog fence in my front yard, which is 1/4 mile off the road. Most late afternoons the birds hop the 4ft fence and hang out in the front yard eating bugs. Sometimes my dogs are out in the front yard at this time and they don't mess with the chickens. However, if I see the birds hanging out in the dog fence and the dogs happen to be out, I bring the dogs inside so as not to tempt fate.
You will need patience and discipline. If your dogs respect YOU, they will respect what is yours, so claim the chickens as yours. For the first month I wouldn't even allow my dogs to LOOK at the chickens without getting fussed at. My rat terrier still won't look at them, which is fine with me. I don't try to make them friends. I just want the dogs to realize they are completely off limits, just like my food. The 5 yr old likes to try to lick their heads though. He's completely fascinated with those birds and wags his tail happily when they waddle by. (he's the sable GSD in my profile pic)
A lot of GSDs are wonderful with all sorts of animals - I had one that wouldn't even eat a mouse in the house, but find them out in the field and he gobbled them like candy - and some are just never going to safe running loose around chickens. Even one that will be great with chickens will still need training to understand they're not to be herded, played with or chased. Good luck!