Hi. Sorry to hear your woes. I was in a similar position with my Archie. I’ve copied and pasted bellow a reply I previously posted here about his guarding as I’m pushed for time at the moment. But just wanted to say it is possible to come through it! Do also look back at my previous posts where you can see how bad things were and how far we have come!
It is really important to work out exactly what the root cause is so you can address it. Outside eyes can be useful in spotting things you might miss so bringing in an experienced trainer when it’s possible would be useful.
The only experience I have is with Archie so I'm no expert on the issue in broader terms. Archie didn't have a crate or a pen but I used (and still use) a baby gate to keep him out of harms way when necessary. It's easy to say (but not easy to do, especially when children are involved) but it's vital to try to avoid the situation arising in the first place. Nothing can be left lying around. Using a house line can also be useful to lead him away from sticky situations without going near the bitey end.
I know how hard it is to live with a guardy dog and anything that can keep the problem at bay while you work on sorting out the cause is a massive help.
The book Mine is an excellent place to start. I agree with not making an issue out of a guarding situation. My experience with Archie (who's root cause was generally nervousness and anxiety, although he would appear to be very full on friendly and confident - essentially over compensating for his issues) is that ANY kind of raised voice or trying to make him understand that what he was doing was unacceptable was absolutely the worst kind of approach. It re-inforced his worries and made him dig in and guard whatever he had even more. There was absolutely NO way I could remove an item from him without risking serious injury. He didn't back down ever and I learned the hard way that he was not bluffing when he threatened to bite me. My approach was actually counter-intuitive in that if he was guarding something I would gently praise him and tell him it was Ok, then walk away. We worked on him fetching things to swap for his favourite biscuit. "Fetch it for a biscuit" became the trigger to make him relax and eventually he learned to swap even the most prized object. It was all based on him learning to willingly GIVE me something I asked for, not me TAKING it from him.
He is now a really reformed character. He is the most loving, cuddly, gorgeous boy. That said, I know that he will always have that side to his character and I always keep an eye out for it. He rarely guards anything from me (but will occasionally push the boundaries if he is at my Mums house) but he does guard his own sick which is utterly charming of him!!!
It can be hard work but It is possible come out the other side of it.