You said "he passed all his classes". Well I started in classes when my girl
was 4 months old. She'll be 5 yrs old in April and we still train.
Get in another Obed class; introduce him to other activities like Herding or Tracking or Agility, etc. No matter what you decide to pursue, Obedience is the bottom line for anything to follow. It's the foundation from which we build our dogs!
Keep him in-training and he'll be too tired to get into mischief! Good luck!
kathy