Blood work! I think most vets wait until a dog is senior to start recommending it. I lost my first lab 5 years ago to liver failure. He was only 7. I had never done a blood panel on him because no vet he'd seen had ever recommended it. If I had started doing regular blood work on him, say maybe at the age of 5 or so, I might have been able to save him. I know it adds $100 or more to the annual exam cost, and some people won't want to pay it, but at least give them the recommendation.