I had this problem with my Jack Russell, when i took him to puppy training, i was taught how to train him to walk nicely, try holding a treat in the hand without the lead in it, hold it down towards his nose so he can sniff it but not touch, when he has walked for a few metres without picking anything up and focusing on you and the treat, praise him, and give him the treat and plenty of attention, then do the same procedure again but make him walk a little further before he gets the treat and each time you repeat it, raise the distance slightly. this may help, it is also a good way to train dogs to walk of the lead. good luck. :-)