Well since he is still a pup I say give him time. If right now you have to remind him every minute or so that is alright. I would praise him good when he moves on to 2-3 minutes with out a "heel" reminder. Does he get time during your walks to explore alittle? I would think that would help if after say 15 minutes of walking you let him have a minute or two to sniff around then proceed again with "heel". just a thought.