Enrichment: it's important to determine what is enriching for your dog.
Pet Harmony Animal Behavior and Training co-owner Emily Strong CDBC SBA has an excellent blog post When Is Enrichment Not Enriching, and shares enrichment strategies for dogs on a podcast of How Do You Train That?
Emily and Pet Harmony co-owner Allie Bender have written Canine Enrichment for the Real World. The book discusses the origins of enrichment, what it is and is not, types of enrichment and why they are important, as well as creating and implementing your plan. It's an excellent resource!