While it's not getting to the core of the problem, I'd start by not giving him bones or whichever treat he guards. At very least, only give them in his crate where he can't/won't be disturbed.
My dog had resource guarding tendencies. Still does, to a degree, but going through an obedience class helped us bond. He had to learn to trust me and that I was the bringer of all that is good, yummy and fun in his world.

NILIF helps, too.
He guarded certain treats (and only if they were too large to eat all at once) and certain toys (hard rubber balls especially), so he doesn't get those toys anymore, and all treats are broken up into bite sized pieces. Learning "leave it" has helped a lot. And if he manages to pick something up (like a discarded chicken bone) without me noticing, I can now take it off him.