Gio'sMamamia, yes, I agree with you on the socializing; it's best to wait until he's had all of his shots before letting him interact with other dogs. You do want to control his interactions with other dogs to be sure that they are positive experiences for him. Besides what you mentioned, go any place that people walk their dogs. Having the experience of meeting other dogs on a leash for a count of 3 and then moving on is also good for them. Of course, the best place of all for dog-dog socializing is puppy obedience school! And besides, it's fun!
As far as the object guarding, here's what I've learned from trainers and reading. (Joey used to have this problem, too). You want to teach your dog a "drop it" command. Basically this is done when he has a lower value object in his mouth that he isn't like to guard. Offer him a treat when he has something in his mouth. As he drops it to reach for the treat, say "drop it" and give him the treat. Pick up what he has, look at it, and give it back. If he can't have it back, offer something else for him to chew or play with. Repeat a bazillion times, making an effort to give things back to him far more often than you take them away. If it's something he can chew on, when you pick it up, smear it with a little peanut butter or soft cheese and give it back.
You want him to learn that dropping things on your command is a winning proposition for him!
The link Joy gave you is an excellent article on resource guarding:
http://www.clickersolutions.com/art...ectguarding.htm
The small book she mentioned "MINE!" is also an excellent resource.
In the meantime,
try very hard not to chase him and not to corner him. You will make him more defensive. Instead, pick up a treat (keep them handy or on your person) and something to substitute for the forbidden object and walk over. Offer these and see if he will trade. If not, try rolling the treat beside him - as he turns his head to grab it, snatch the forbidden object. This is fair in the doggie world.
Alot of people feel that you have to establish dominance over the dog in these situations. I don't. What worked with Joey is training an alternate, incompatible behavior. He can't guard something if he's following a "drop it" command and getting a treat. We both win.