I've found that when a dog is 'always' on a lead on the few occasions they are let off they don't wan't to come back - can you blame them?
Take him to places where he can run around safe from traffic etc, call him, if he doesn't come run away or even better hide, he'll soon come looking for you, cheese is a good treat, when you get him him on the lead don't go home, walk round for a few minutes then let him off again. If he associates the lead with going home and not having any more fun then can you blame him for not coming back?