Originally Posted by Shropshirerosie
If it were me with this dog, I would try the following:
Stop allowing him on your bed, or lap, or sofa etc; stop letting him 'cuddle into you' and emotionally claim you. I would continue to show him love, but only with his four paws on the floor, and only when you initiate it, not him.
I would make a point of demanding good behaviour and respect - sitting or lying as appropriate when other people come into the house, and I would not allow any kind of territorial behaviour. By which I mean barking, growling, space-hogging etc.
I would hope to see a change in behaviour fairly quickly as his place in the household is changed - but I would also expect him to want to take back his former role, so would always be on the look out for him trying to be the top male.
IF there was an improvement, I would consider fostering him out to an adult only experienced home with full discussion of his mentality and history.
Oh, and yes, I would most definitely have him neutered properly. For his sake as well as yours.
First off, I have never heard of the neuter injection for dogs (only rabbits, etc.!), but he does definitely need to be properly neutered if all the injection does is makes him unsterile. By not being correctly neutered, he is still going to act like an intact male dog, which could lead to aggression (mainly towards other dogs), dominance (of other dogs and people), possessiveness/protectiveness (especially of humans, as you are experiencing now), etc.
Secondly, I agree with most of what Shropshirerosie said. The dog needs to learn that his family and visitors are in charge. When visitors come into the house, he should be on-leash and sitting or laying down on a "spot" where you tell him to stay. He should not be allowed to rush up to the visitor to say hello, and he must remain calm before the visitor bothers to say hello to him. It does sound like he is being protective of you. In that case, he is to not be allowed on the bed (couch, chair, etc.) where you or your visitor is sitting. If he jumps onto the bed, get him off immediately. If he does so and acts aggressive, dominant, or protective, get him off imediately and put him on a "spot" again, where he is to sit/lay until you say otherwise. If he is crate trained, do NOT use the crate to punish him. In locking him out of the room like you did or putting him in the crate, you are more or less just ignoring the issue and not addressing it. By allowing him to sit there and growl at your friend through the crate, he was escalating the issue while you were not properly corrected him, and he still got his way.
If you are walking around the house with the visitor and the dog acts up, do the same thing I mentioned above in sending him away to sit/lay on his "spot". At this point, it is best if you are the one to correct him, not your visitor, since he will still be learning what you are expecting of him.
I do not know the severity of the situation so can not comment on what type of home he should be placed into. IF in fact this is the issue (being protective), informing his adopters of the issue is a must, even if he seems fine when being adopted, as the issue may return without proper managing of the behavior.