Dog walking is great, for the pooch and for the owner too. I try to get at least 10,000 steps a day, and much of that is from dog walking - in the morning, and especially, late at night. My dog appears to be truly nocturnal - he's sluggish and lazy during the day, but once night falls, he's springing up and down when I get up and grab the leash. His primary motivation is marking - every other tree, pole and free-standing object, it seems.
I've wondered how things would be if humans' concept of property ownership were the same as dogs' - you can only own what you can pee on, and only for so long as someone else doesn't pee on it. Then you've got to go out and reclaim ownership, day after day after day.