he, and the other cavaliers who do agility where we do flyball just look scrawny (even though they are the ones who are actually the right size).
Yes I know the feeling -- sometimes people ask why my cavaliers are so small. But it is a perception issue -- they are all just average size, all but one within current breed standard size, and all in good (low) weight). It's all about exercise and limiting their access to food. Unless a dog has a serious issue like a thyroid problem, losing weight isn't hard (especially compared to our own human struggles!) == just don't feed as much. After all we have the opposable thumbs, not the dogs. If food is safely stored, they can't get it out of cupboards, containers or refrigerators themselves.

With our dogs, as with children (as pediatricians say) -- we do seem as societies across much of the developed world to have had our visual fatometer skewed to where we view overweight sizes as normal and tend to see obesity as just being 'a bit overweight'. This presents as much a health risk and life shortener to dogs as to humans and is as much an epidemic with our animals as it is for us all.