Protective Aggressive Behavior

Question
Hi Labman,

My husband and I are looking for help.  Our 4 yr. old lab, Cooper, is getting very aggressive.  He has always barked and/or growled whenever anyone came over or even went by the house but he's never gone after someone... until last Monday.  I was in the house and my husband was on our deck with him.  A car drove into the driveway and Cooper starting growling and barking.  My husband told him to get into his kennel and stay.  He is usually very good about doing that.  A man was coming to read our meters.  After he got out of his car, Cooper ran at him snarling and barking.  Scared the you-know-what out of all of us.  Thankfully, Cooper did not bite him but he came very close.  My husband was able to get him under control and locked into his kennel.  It was an aweful experience.  We just can't believe that our sweet little boy could turn so vicious.  We can't take the chance of him hurting someone and obviously we hope we don't have to put him down.  And we don't want to have to keep him locked in his kennel for the rest of his life.  Is there anything we can do to change this behavior?  We can't think of what we might have done to encourage it.  It was stupid of us to ignore the warning signs.  We should have done something about it when we starting realizing that there might be a problem.  Since he was a puppy, he's always been a little strange.  Usually, when you're dog sees you, they're all happy and wag their tail.  Not Cooper.  He'll just look at you, not moving, until you get right up to him.  Then he'll go blalistic and smother you with kisses.  Is there any help to change this?  We love him dearly but don't want to take the risk of him hurting someone.  Thanks for your help, Carrie  

Answer
As dogs mature, it is quite common for them to take more responsibility for the protection of the pack.  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/

This may be a more severe problem than you can solve working out of a book.  Even many obedience instructors may not be able to help you.  If a class doesn't solve the problem, try individual instruction from a dog behaviorist.