Growling/Snapping

Question
We recently rescued a 2-3 year old choc. Lab.  We have had him neutered and he is 100% house broken and seems to be a great dog (other than a nasty ear infection).  Recently I attempted to get him into our garage while we were going out and he refused to go.  I tried to toss a bone into the garage he still wouldnt go.  I reached for his coller and he growled.  I nsid NO GROWL! and reached for his coller.  He snapped.  I instinctively smacked him on the nose and he came at me with teeth bared. I put my foot between us and he bit through my shoe cutting my toe.  Is this a "fixable problem"?  I have two young children that I am very worried about.

Answer
That is really hard to say.  His personality is nearly mature now, and will be hard to change.  Best thing is to get him into a good obedience program.  
Having a good pack structure reduces such problems.  The 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/  If you can find a good class, it would help a lot.  There are things an instructor can do in person that is harder for me to do over the net.