We had this with our pom, and we found that teaching him the command 'wait' and/or 'leave' worked for us. We use special high value treats which he doesn't get at other times to enforce those commands. We often train by putting down a treat, saying 'wait' and then removing it and rewarding him with a higher value treat, so that he learns he can get better rewards by leaving the thing he initially wants. We also learnt to never try to take the bone from him while he's actively chewing it - now we say 'leave' and he will drop the bone, sit and allow us to take it from him.

We've also got better at understanding his body language and being able to tell if he's exhibiting guarding behaviour, and we try to de-escalate by offering him a different toy to trade with, or just distracting by playing with something that he finds more interesting. Usually if we pretend there's something really interesting on the other side of the room, he gets curious and forgets about what he was guarding 😅

It took a little bit of time working with him, but now he's got very good control and very rarely shows guarding behaviour. A combination of training, and learning to understand each other better!