Older dog stop playing with puppy.

Question
I have a 6 year old lab/shephard mix and a 6-month old rottweiler.  We have had the the puppy for 3 months.  Initially my older dog didn't want anything to do with the puppy, but after about a week they became buddies.  Now after three months my older dog has become more aggressive with the puppy and growls at him everytime he trys to play.  I am not sure how to handle it.  My puppy is moping around because his buddy won't play with him, but even if I get them to play together, my older dog eventually gets aggressive and scares the puppy.  I am beginning to think they are both afraid of each other but for different reasons.  I guess my question is, do I leave it alone and let work itself out, is there something I should be doing differently, or do I need to get a trainer in to work with both of them.  Any help you can provide is much appreciated.

Answer
By the time many dogs are 6 years old, they lose interest in puppy biting games.  The Rottweiler may be as big or bigger than him now and challenging him for pack rank.  I would support the older dog's lack of interest in play.  Right now I have my 14 year old Aster exiled to the living room behind a gate so I can have a break from correcting 9 week old Xanthe for bothering her.  I can remember when Aster was about 6, she and her mother would play together a little, but neither one of them played much with other dogs.  

It would help if you gave them both stronger leadership.  The key to most behavior problems is approaching things using the dog's natural instincts.  Dogs see all the people and dogs in the household as a pack with each having their own rank in the pack and a top dog.  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/  For more on being top dog, see http://www.dogbreedinfo.com./topdogrules.htm