I teach basic obedience training to dogs ranging in age from 8 weeks to 7 years. Dogs older than 7 years are seniors and should be allowed to do pretty much whatever makes them feel good. :D
I use only food and a clicker for positive reinforcement. I do NOT use - nor do I allow the use of - prong collars or physical force of any kind. My philosophy is that where there is mutual trust and respect between a dog and their human, force is never required.