There is a difference between adding duration to the sit or down command and a "long-down," where the dog learns to go to its dog bed and staying there while you watch TV or work in your office.
The art of accomplishing a "long-down" begins with a good foundation in the sit and down exercises. Once the dog understands the meaning of the exercise, then duration is added. In the beginning, duration means the trainer stays close to the dog. The dog needs to learn to hold the down when it is on a 6 foot leash as the trainer moves and holds the leash.
Before a new trainer can consider a "long-down" with the dog on its dog bed, he/she needs to be sure that the dog will stay down when we add in distractions while it is on-leash.
This video came directly out of our new Basic Dog Obedience DVD and online course.