Can you recommend videos or books for training a Doberman?

Protection training (like all dog training in my opinion), is not breed specific. In other words, we do not train a Dobe any differently than we train a Rot or a German Shepherd. Training varies according to the temperament and drive of the individual dog and not its breed.

So the job of the handler is to recognize prey drive, nerve levels and hardness (or softness in a dog) and adjust the training accordingly. This is not an easy task for new trainers.

What I recommend is the new trainers begin with Bite Training Puppies and then The First Steps of Bite Training. These 2 videos are going to get new people on the right road. They are far from everything that needs to be known but they are a good start in the right direction.