I am taking my 1 year old Border Terrier to dog training classes. He is stuck in the same group level as he just will not lie down (drop command). He can do everything else but can’t grasp what is wanted here. At home he lies on his side or lolls around on his back. I have never see him take the position that is expected so can’t even reward him for accidentally doing this. All the other dogs seem to sit in this position quite naturally and comfortably. Any tips?