I think the two most important things to remember when starting out with a new dog are: Training must take place daily, every time you go out with the dog and indefinitely. And never leave the dog alone or otherwise allow access to the chickens for a very long time. I raise and train my own ranch dogs and they are livestock trustworthy dogs but it takes a long time for them to get to that level with me and honestly, I still don't trust any dog 100%. My chickens have a coop/run and have access to my securely fenced, dog proof pasture. I have a couple of birds that like to come up to the house occasionally and my dogs ignore them completely but they don't share space on a regular basis, especially not when I'm not around.
As far as any breed being trainable to be with chickens, I somewhat disagree with that. While there are shining examples in any breed of dogs who are good or terrible with chickens I think it is only fair to consider a dog's inherent traits when considering breed. It can certainly make your job easier at the least. There are some breeds with naturaly strong prey drives, some breeds also respond better to training then others. Not all breeds are people pleasers etc. It's just worthwhile to take all those things into consideration, especially if a dogs past is unknown.
ChickensRDinos methods are pretty much what we use here and with great success. Daily exposure, rewarding good behavior and discouraging the bad. Eventually a dog who is going to be good around chickens will get bored with them, it will all become everyday stuff. A dog who is not going to get to that point will show you by it's actions and continued over interest. Although you will often read stories on this forum about the family dog who was always great with the chickens.... until the day he wasn't.
Good luck, I hope you find the right dog for your situation. With care and diligence you can turn out a good dog who will respect your chickens.