I recently went to a behaviourist seminar and she talked about this and she advocated using the 'behind' command. To get this she would put the dog behnd and hold the lead behin the back then every time the dog tried to come forward woudl block and say behind. It takes a while and you look a bit silly at first but i have to say it worked. Eventually you can just have the lead at your side and still have the dog walking just behind!

it worked wonders with mine!!