well its obvious that he isnt comfortable with the lead yet and so he is tolirating it for so long then decidng he wants to be off lead and just stops, the best way is to put his lead on him and just let him walk round the house with it on watching him of course incase he gets tangled, that way he dosent associtate the lead with being dragged along outside. Once he used to it he shudnt have a problem, just make sure you dont drag him as like you say its pointless and he could get sore pads.
hope this helps
