Lazy?

Mr Alfred Dog has taken it upon himself to start refusing to go for walks with me at all (forcing me to carry him to a tree to do his business), unless it's somewhere 'special' like the woods, or the wild animal park, where he runs about like a young pup the whole time...  I wonder why this is - even in the lovely bright sunshine he won't walk in the neighbourhood, but the minute we're back inside he happily runs about with his ball like a crazy thing.  It's a bit worrying to be honest. :-(