He's nervous about anyone coming into his territory, so having something in his mouth is how he deals with the stress. Think of it like he's say, "This is MINE and you can't have it!" Sometimes dogs deal with this kind of stress by eventually escalating to biting to make the "intruder" go away.
You can either continue to support that behavior, or try to help him become more confident. The idea is to get him to see YOU as the one in control of who comes into the home. If he trusts you as a leader, he won't get stressed out and obsess over having something in his mouth - whether it's a toy or a body part. LOL!
Can you describe in detail how both you and your dog react when someone knocks on the door and is invited into the house? I might be able to give you a better idea of how to handle this behavior if I can get a better idea of what is going on.
Easy fixed all my dogs do this.He needs toys mine, have heaps.They are like children they need something to play with something that belongs to them.
They are gundogs and must have something in thier mouth.
When people come around it is a form of greeting..... when I go out and then return all three look for thier balls teddy bear to show me ....,its like look at me and what I have got.
So go and get him some rubber balls and if he does not rip them up some fluffy toys from the Op shop.
He will be in heaven,. You have a real sweetheart of a dog..... he just needs something that he can show everyone! my dogs have a toybox they share so they pick out thier own toys.
Some times i get them a new toy each. Well all three marching around as pleased as punch with them.
Have fun.
its a territory thing i think. it s like hey this is my house and these are my things. i dont think ts anything to worry about, if your worreying about the bowl, try placing a few of his things by the front dor so hell grab them first.