OPPS ! I did not realize you were so well informed about training. LOL I feel bad for going on and on and on.... So you already know what is going on and just need a few hints or maybe a new idea or two. I think you can stop the treat guarding simply by only giving,
one bite size treats, you know like the size of a pea. Gulp , and it is gone, nothing to guard. When you give Chew type treats, or stuffed Kong toys, only let them have it in their crate. I understand all about the Lab pup. I used to raise and train Labs. I have 4 Yorkies and a big old Lab now.
Of course you know you can interrupt behavior with a surprize sound, touch, or visual distraction. I bounce a tennis ball, or toss it near the the dog. I am very careful about telling lay people to toss the ball near the dog, once a man threw the ball hard and hit the Yorkie, I almost ran over and hit the man on the head with the darn ball ! That is why I suggest rolled up socks to toss.
Anyway
I will skip the 7 day Rehab I use. I suggest, to just go back to your basics, be the leader and nothing is for free. Teresa