agression towards dogs

Question
In my home I have 8 year old retriever mix, 3 year old chow mix, 2 year old Pyrenees mix (Deja) and a 7 month old Heinz 57.  My 3 older dogs have gotten along fabulously until about 3 months ago. While i was walking all 4 dogs the Pyrenees attacked the 2 year old chow two days in a row. It was fairly severe but luckily only had one minor cut. Since then the Pyrenees has been very difficult to live with. She is constantly stalking and attacking the youngest and the chow. The puppy hides now when she sees the Pyrenees coming. It seemed as if food was a trigger so we took measures to prevent these attacks but now the attacks seem to be occurring more frequently and without provocation. I have taken Deja to the vets for blood work which was normal. We have had her on three different psych meds, none seem to have any effect. We recently added valerian root but that too hasn't made an improvement.  For a little history-we got Deja from a rescue group as a puppy - her mom was severely malnourished. Deja has always exhibited unique behaviors, excessive licking of the human family members, severe submissive urination for the first 20 months, refusal to toilet outside if the ground was wet, generally a bit on the skittish side, and continuous seeking of human attention.  She had previously played great with the other dogs, now she wants to control all of the toys.  Until i adopted my first dog 8 years ago i had no canine experience. I have certainly made my share of mistakes raising them but do know now that i need to be the leader of the pack and the other pooches are fairly well behaved.  I am at a loss with what to do to bring peace back into the family.  Any advise for specific training ideas or medications would be greatly appreciated.  Thanks, Debra

Answer
Are all your dogs spay/neutered?  It can make a big difference.  Even if so, the gender can make a big difference.  If the other 2 dogs are females too, they may be maturing and challenging Deja's place in the pack.  You may need to provide better leadership and correct challenges to Deja.  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  Correct the younger dogs if you see them treating Deja as a lower ranking dog.