Hi Sarah!
I've got a rescue dobie too, got him when he was 3, he's now going on for 9 and still acts like a silly little puppy.
Dobermans are very strong willed dogs, mine has a strong predator drive, but an even stronger will to please those he loves, family and friends included.
The first step to introducing any dog to what could look to him like a potential dinner that's fun to catch is to have him or her under control. Obeying a stop and then a down order, basically being able to cut an excitement short at any time.
When you have that mastered, take your doggies for a nice long EXHAUSTING walk, or even better, a bike ride. When they are nice and tired, introduce them to your flock through the fence, or even better on a leash, with or without an educative collar (that tightens when you give a short tug).
My dobie has uncropped ears, so it's easy enough to know when he's too interested in something, they turn into satellite dishes. Any excitement, whining, staring, tail out straight is something we don't want.
When they get too interested in the flock, fixating on the girls, say a big "no" or what ever you use to scold them, sharp tug on the leash, out of the coop, down and one minute time out.
Repeat as often as necessary, with my Disco it took a weekend, could be less, could be more.
When they start to stop seeing the birds as prey, leave them just outside the coop, and let them see you caring for the hens (petting them is a big plus).
Progressively, and as your trust in your new pups increase, you will be able to let the hens roam around them, the dogs staying down the whole time.
I've had my girls for three weeks, and my big boy ignores them completely. I would never trust him enough to leave them together when we are away, they both have their separate spaces for then, but last weekend everyone was happily sharing the garden and terrasse with us.
Good luck with your doggies, they truly are an amazing breed, and let us know how it goes along the way
