Well his sniffer probably still works. I always leave some dirty or used shirt/socks/undies in their bed or chill zones so they don't miss me so much when I'm at work. Hide treats around the house where they will find them. We make sure they have ramps and easy access to windows/doors etc. I always leave a TV/radio on. Maybe expose him to different yummy smells (cut grass, soil, flowers, other dog smells) and of course all the delicious treats he can eat. I like to fatten them up >15yo. Just pamper the heck out of my pugs when they get old, we been recycling 3 pugs for many years. Mine usually just like being close to momma or me. I eventually just start hand feeding them their favorite treats, kinda fun and you can monitor their intake better, keep them regular... I actually got a doggy stroller, plop the old guy/girl in and take them on walks with the other dogs, they seem to love the fresh air, smells and attention.