My toy aussie is overprotective

Question
I have a Toy Australian Shepherd and he is going to turn 3 in november. I
know Shepherds usually are protective and guard dogs. When we first got
him, he was a very shy quiet dog but as he got older he began to come out of
his shell and started becoming over protective of our family. He is a very
friendly dog to the people that he knows, very sporty and loves to give kisses
and be playful, but when strangers come close to our family thats when
things change. Like for instances when we have guest over he will bark at
them until we greet them and then he sees that they are not a threat. Then
every time some one is about to walk out the front door, as soon as they turn
their backs to him, he starts barking and going a little crazy. When we are on
the sofa relaxing and someone other than ourselves comes close to us my
dog will start to growl and snap at them. If we are on a walk and he sees
people coming near us, he will start barking and maybe want to attack them,
he will try to run after people on bikes or even cars. With other dogs he
sometimes is playful wit them but other times he looks ready to attack. Any
suggestions on how to stop him from being so protective?

Answer
This is common in herding dogs as they reach maturity at 3 years old.  it may be too late to do too much.  With stronger leadership, he may allow you to deal with the strangers.  

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