I would say put the lead on and go for your walk .As someone previosly said short sharp tugs on the lead to remind him who is in charge if he starts messing.Off you go on your walk but if the short sharp tugs are not working turn around and go in the opposite direction. He will soon get the message or should. My niece had this problem with her dog She got a dog trainer in and this is what she was told It worked very quickly
Hope this helps.
Angela