It depends on your dog and your lifestyle! We personally don't walk our dogs that much.. probably a couple of times a week for 20-30 minutes. But we have a pretty big house that they get the run of, a backyard they get to run/explore in, and a playmate (my roommate's Chihuahua) to run around with. They do pretty well and spend most of their time relaxing on our couch.
I know other YT members walk their dogs for hours and miles at a time! I wish I had the time/energy to do that.
