agression in the house towards visitors

Question
We got our Shasta(male) when he was 3 month old,he is now 13months old,he has been since the beginning fearful of sounds and new things.We have taken him to puppy kindergarten and also let a trainer have him for 2 weeks to work with him.The problem we have with him is when someone comes in to the house,they may be new or they maybe someone who has been here many times,he gets all excited and barks and does a 'coo-joe" act which is growls and lunges at them,I can't say he will or won't bite them.Our trainer wants us to redirect him by sitting him and then heeling him,otherwise take his mind off the person.I find if I let the person come in and let him approach the person,after I make him sit and he calms down it works better than holding him on a leash and heeling him.But not always,the trainer says we have a territorial,fear dog,he can be such a cutie,I want to know what the best way to approach this situation? He does sit,lay and stay,although we are working on it to make it stick,because its not a guarantee he'll listen.

Answer
You need to get a grip on this immediately.

What I'd do is make him sit and not allow him to "greet".  If he moves, herd him back with your legs.  Have guests come in and TOTALLY ignore him.  Not even eye contact.

The key to training is to anticipate and correct before the behavior happens.

So after guests are in and seated...he's still not allowed to approach.  Be calm - matter of fact and just keep returning him to his Stay position.
Delores