I always tell clients that if they do not practice the behaviors that their dog has learned, then the dog will forget those behaviors. It is like learning Spanish and then never using it. I took 2 years of Spanish in High School and can barely speak but a few words. After high school I joined the USAF and never needed it. Now I work in a school with many Spanish speaking students/families and wish that I had kept up with my Spanish.
So, a dog can very easily lose those fun amazing tricks/ behaviors that you worked so hard at teaching, if you do not practice them with your dog. Keep your dog on his "A" game by continuing to practice and work on all those behaviors that he knows. By practicing the behaviors/tricks he will stay sharp and you can continue building that bond and closeness with your best friend (your dog).
Keep a journal of the things your dog knows, so that you can make sure to practice everything. Change it up by practicing in various locations with many different distractions. Challenge your dog and keep his mind mentally stimulated.
"A mind is a terrible thing to waste!"