My 10 month old dog won’t bring the tug back when we play, he flops down and holds it between his paws. Do you have any advice?

Hi!

I have a 10 month old gsd and we have been working on our tug game to eventually incorporate it as an obedience reward. I have purchased the Michael Ellis dvd on the Power of Playing tug with your dog and I am continuing to study it. I am very pleased with the course. The issue I am having with my dog is he won’t bring it back and I have studied the video where Michael demonstrates to tug a few times, let him have it, and encourage him to take even 1 step toward you, mark and play again. However my dog is wanting to go off and lays down with it between his paws not wanting to bring it back, which I assume is possession. I try encouraging him with noise, praise , and slight leash pressure but he isn’t wanting to budge. He loves the tug and chasing it and tugs with intensity but struggling with this. I did see in the dvd troubleshooting dogs that don’t want to out or that may be running away but none that were flopping down to prevent them from having to bring it back. Any advice!!