I can't get Diesel to hold things. For instance, a bag. I've tried bags with different textures, thick handles and thin handles. He will mouth them, take the handle right up to his back teeth, but as soon as I let go he drops it. Today when he put it into his mouth I tried to wind him up and pull it back and turn it into a tug of war, he did get a better grip on it but then as soon as I let go, he drops it. Any tips?