Hi ,
One thing i have found that works is if you tickle their bums while your walking.... I actually learnt it off the dog whisperer so i cant take the credit ha ha...
During the episode he had a small dog, older dog , who would not walk when on a leash, he would just stand there and pull back on the leash.. Ceaser suggested the owner walk beside him and tickle his bum hahaha... it worked for this dog and has also worked for my boxer lab cross who was having the same problem a couple weeks ago..
I cant honestly say why it works but it gets them excited and they start to move hahaha... it only took me a day to get bella walking normal again
Hope it helps - i know it sounds weird hahaha.