Unfortunatly, I think you unintentionally started the resource guarding problem by 'constantly' sticking your hands in his food and taking away his toys. What you are doing is an old school technique that only works on dogs who would never be resource guarders to begin with. In others, it creates a resource guarder. Always trade. Never take. You have taught him that you will take his things, therefore he needs to protect them. If you don't take them, he learns there is nothing to fear.
It is natural for a dog to protect what he perceives as his - especially something high value, like the bone he found. Your friend put Jax in a position to fail. Jax should never have been allowed off leash. This would not have happened, if Jax had been leashed. I'm sure there were plenty of signs and your friend needs to learn to read them. We were all new to dogs, at one time. It is a learning process. Your friend can do this.
Teach Jax the commands to 'Drop it' and 'Leave it'. Keep him on a leash, until he has a rock solid recall. Learn Jax's thresholds. Watch for signs of discomfort - body stiffness, lip licking, whale eye, etc. I'm sure some of those signs will be there. Start to desensitize him, by only trading up and never taking his things without reason. Respect his threshold and you will see improvement.
My Natty Boh was a pound puppy and a terrible resource guarder. He would bite, if pushed. He is a hound mix. I hand fed him every day for months. I never, ever bothered his food. Once I sat it down, I didn't touch him or his bowl. (He also guarded toys, antlers, his body, his space) He is 5 years old now. He tends to be a very snarky dog, but he doesn't bite any more. I doubt Jax is as bad as my boy. lol! I hope your friend can get over his fear. It is not pleasant to get bitten and I'm sure he takes it personally. Assure him that it isn't personal and is something that can be corrected.
I am confident you can turn this around.
Natty Boh 6-27-12
Annie 1998 - 8-2-12 RIP
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