I don't get why he would even want to go jogging. These two fight demons, witches, vampires and whatnot on an everyday basis. I'd say that's enough workout.
This may sound weird but your comment actually inspired me to see if there are any water aerobics classes in my town since I need to lose a bit of weight. There's one like a 10 minutes walk from my house lol I'll probably sign up
Not only knees but also ankles and hips and basically all your joints