New second pup

Question
I bought a Retriever/Shepherd/something else puppy from the Animal Control Shelter.  He was four months old and I have had him for one week. He is neutered.  I adopted him as a companion for my other dog (a 2.5 year old female greyhound mix), who is was spayed and who also came from the shelter (we got her when she was around five months old).  

Here is the issue:  our female (Vanessa) is pretty dominant.  She loves to rough-house with bigger dogs. She is also a bit possessive over her toys (she doesn't fight other dogs for them, but steals and barks at them until she gets the toy back).  

We took Vanessa to the shelter to meet the pup.   He was very timid and submissive, so we adopted him.   Naturally he warmed up and has started to adjust to his new home.  Lamont (the pup) is still a very sweet dog.  However, he is beginning to show some dominance toward her.  For instance, he doesn't know how to puppy play; generally she will initiate and pull his leg, etc, and he will let out a warning growl or chase her.  She will usually run away and try to make a game of it, but I don't think he's catching on.  Plus, he doesn't "play bow" like she does.  However, she will assert herself (i.e., sniffing, etc) and he will generaly stay still.  But I am concerned of a serious dog fight between the two because there seems to be some tension between them as though each is trying to establish who is top dog.

I am trying to establish that he is subordinate to her without having her be overly dominate to the point that it causes problems.  For instance, I will greet, feed or approach her first.  I also try to let her go outside/come back in first (after me, of course).  But I don't know what I should do about the playing. I want them to play together, but how should I supervise the play?  At what point should I intervene?  Thank you for any advice you could give me.  

Answer
I encourage people to adopt.  However, sometimes adopted dogs come with difficult to handle baggage.  If he was removed from his mother and litter too soon, he may not have learned how to get along with other dogs.  Such mistakes are not easy to correct later.  Keep a close eye on things.  Sometimes it is hard to tell what is going on between 2 dogs.  Hair on the back up, low growls, and a wrinkled nose are bad signs.  Quick snaps or running off and not coming back are bad signs.  Since they should be about the same size now, they are unlikely to seriously hurt each other.  Watch for any broken skin.  

Obedience train both.  He is not too young.  You may even be able to get him into a puppy class soon.  If you are top dog, you can insist on peace in the pack.  Life is much easier if the 2 legged pack members
outrank the 4 legged ones.  You can learn to play the role of top dog by
reading some books or going to a good obedience class. A good obedience class
or book is about you being top dog, not about rewarding standard commands with
a treat. Start at http://www.dogsbestfriend.com/