5 year old aggressive lab

Question
Our 5 3/4 old Yellow Lab (AKC) is aggressive upon first meeting of other dogs(any breed, size, etc).  Although, after a day or so around this "new" dog, she is usually good.  She is great around people, kids, and even (after a short time) around our new 5 month old Yellow Lab (AKC).  I assume that this is some sort of "Alpha" behavior, but I really want to fix this before it creates an even bigger problem.

Thank you

Answer
At 5 years old, fixing it may  be tough.  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

That may not be enough.  You may need a professional trainer or behaviorist.