aggressive behaviour

Question
I'm looking for some direction on what we should do with our 6 year old male
Shepherd.  We have had him since he was a puppy and he is a great dog.  
He's quite dominate with other dogs but never shows any aggressive
behaviour
towards them other than to steal their sticks etc.  When he's been out playing
with a couple of our nephews he has a tendency to nip at their ankles, I'm
assuming this is an instinct of his and don't really consider this aggressive
behavior although I would like to prevent it.
We had  a baby 16 months ago and ever since then, he hates one of the paper
boys who comes to our home.  This boy has been coming for years and
before the baby used to play with our dog in the yard with no problems.  Now
our dog has started to growl and nip at him and this past week, he went after
the boy and  actually bit his leg in a very non-friendly manor.  There are two
paperboys, brothers, but it is only this one he has a problem with.  We have
left a msg for the boy's parents to call us but so far have not heard from
them.
I'm just wondering if this is a warning of  behavior to come or if there would
be a reason why he would act this way to just one boy.  Mostly, can we still
trust him around our daughter or other young kids.  We love our dog but do
not want to risk his harming anyone else.

Answer
Neuter him if not already and then obedience train him.  Even then, at his age, it may not be enough.  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  See their page on dogs and chldren too.