When playing tug and I let my dog have the tug, he runs away with the tug, sits and tries to just chew on it. How do I get the dog to bring the tug back once I let him have it?

I've watched the DVD on The Power of Playing Tug with Your Dog. I have a 5 month old dog and I use a tug to play with him. He sits, outs, and listens while playing. However, when I tug back and forth for a bit and then let him have the tug, he runs away with the tug, sits and tries to just chew on it. I tried putting a leash on him, and pulling him back, but Michael Ellis in the video was telling the new trainers not to do that. How do I get the dog to bring the tug back once I let him have it?

Thank you