Looks like you've been waiting awhile for a reply. I'm a newbie, but when I try to walk Ruger on a leash he just sits down and won't go anywhere. If I take him to the park with my girlfriend and her dog he will follow her dog and poop and pee all over the place. At some point he just sits down, but my girlfriend's dog is a lot bigger and stronger, so I think little Ruger just runs out of gas.
Maybe a "play date" with a friend's dog, both on leashes, will help.