I'm so sorry.

Resource guarding is scary stuff.
Peggy does it on occasion and she is absolutely NOT herself when it happens. Her eyes glaze over; she's operating on a very primal level. Once she is "released" from the fear that her treasure will be stolen, she visibly shakes it off and actively tries to appease me. The one time she guarded a chew (it's usually super random stolen items, like a clump of grass or a piece of bark) she brought it to me a minute later and kept
nudging it into my hand.
In his own doggy way, Coco is sorry. I promise. I find reading Patricia McConnell very soothing:
Years ago, I took care of a gooey-sweet adolescent Border collie, (Tilly, I’ll call her) who flattened her ears and folded like a bird’s wing every time you said her name. She was responsive and polite, and the other dogs seemed to like her as much as I did. It was especially rainy when she […]
www.patriciamcconnell.com
I agree that it's time to find a trainer if you haven't already. Coco has now crossed a line and may be more likely to cross it again now that he has reason to believe his non-confrontational signals (stiffening, growling, etc.) don't work.
But proceed with caution. You want someone who has studied animal behaviour, like cowpony said. You don't want someone coming in your front door, spouting stuff about showing Coco "who's boss." Resource guarding is
not a dominance issue, so keep that in mind as you proceed.
If your vet can't recommend someone, call around to other vet clinics as well as your local animal shelters.
I'm actually "attending" an online resource guarding seminar in December. It's the first three Saturdays of the month, and you can watch live and/or view the videos for one year afterwards. Let me know if you're interested and I'll message you the info.
My fear is what happened to you today: That Peggy will guard something dangerous and I'll have no choice but to ignore her warnings. You were in a very tough spot.
I recommend keeping something extremely high value on hand at all times. This is wise even for those whose dogs
aren't known resource guarders. Then just toss! toss! toss! Keep tossing a little further away until even a clever dog like our poodles can't resist.
And keep in mind that this is only for an emergency. Generally speaking, it's good to pick your battles and give non-dangerous items right back. I sensed that wool dryer balls were getting a little too high value for Peggy, so I practised this regularly. Now she
brings them to me, so it really is possible to make progress, even if it's just baby steps.
Keep in mind, too, that Coco is at a very mouth-oriented stage in his development. It's maddening how much they will pick up and "explore" with their mouths through puppyhood and early adolescence.
Have faith. Sending hugs.
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