Over the years he has gradually become more and more defensive of his crate.
The rule has always been that the dog's crates are their sanctuary. Nobody bothers them when they are in there. The other dog's crate is in a different room.
Whenever anyone approaches the room his crate is in he growls. If we walk in and audibly pick up treats, he will come out to see what we have and then go back into his crate and growl again.
Today, I came in, he came out for treats and a fuss then went back into his crate. He started growling and I picked up the log back to walk past the crate to the back door. As I was opening the door, he lunged out of the crate and bit the bag several times aggressively. The bag was between me and him.
Once the door was open, he followed me out and trotted up to the log store with me, sniffing around, wagging his tail and happy to be with me and next to the bag.
Is there any way to stop this behaviour escalating further? I'm worried he might bite a person soon.
He is muzzled when out and kept away from small children.