My dobie lets our puppy walk all over him

Question
I have a 3-yr old doberman (Rusty) who has always been a gentle and kind dog.  We just recently adopted a beagle/lab mix puppy.  The puppy, Camper,  is very active and playful. We expected all the new puppy behaviors from Camper, but were not expecting the toll it would take on Rusty.  Anytime we play fetch with the two dogs, Rusty lets Camper take the toy away from him.  When we correct Camper's behavior with firm "no!s", Rusty runs off and hides in the closet.  When we play with the dogs, Camper will snip at Rusty, but Rusty never growls back at her or stands up for himself.  I wondering what to do to help Rusty.  Do we need to help Rusty establish the alpha role?  Is he just getting used to the puppy like we are?  I'm wondering if he has low self-esteem or may be unable to share the house with another dog.  Any advice would be helpful.

Answer
Your first job is to stop using the word "NO".  Have you ever seen the T-shirt with a puppy on it that reads: "hello, my name is NO, bad dog"?

Rusty appears to be tolerating the puppy's behavior.  He has what I would call a "soft" temperament, not because he's not putting the puppy in her place, but because of your description of his "closet" behavior!  The fact that Camper is female might be a factor in this even though she's very young.  It's unusual for a male dog (even neutered) to not defer to a female dog (especially an intact female.)  In normal dog pack behavior, you will see males (with good temperaments) tolerate many behaviors from young pups that females will not.  I don't take this necessarily to mean that Rusty can't tolerate Camper and won't adjust to her.

I would not at all interfere with the rank development between these two dogs BUT...I would definitely pay attention to Rusty FIRST at all times, let him in and out first, feed him first, give him treats first, and spend quality time playing catch with him alone, without Camper.  I would also establish some psychological rank over Camper YOURSELF by teaching her a simple obedience trick, like "sit", and expecting her to earn her treats, her food, and even games you play with her, by sitting first.  Don't use the same word that you use to command Rusty; use any word for "sit" not commonly heard, like "tinkerbell".  Use ONLY positive reinforcement training, NEVER an aversive like choke collars, etc.  If you observe Camper beating up on Rusty, interrupt her behavior with a benign sound (like saying "bee bee bee bee bee!".  She will most likely stop and come over to you.  Give her the command you've chosen for "sit" and reward that.

Camper sounds like a delightful girl but her breed combination might make her a handful.  Adopt a new technique, one that works EVERY TIME: reward what you want to see in your pup when she is an adult and IGNORE what you don't like.  Teach her, using positive reinforcement, to shape the adult behaviors you want in her.  Dogs always repeat behaviors that reward them (sometimes these behaviors are self rewarding) and you will almost always see extinction of behaviors that are not rewarding, once the pup gets the idea.