This seems to be a common problem. When another dog displays this habit I normally just stand my ground with my dog. Ask the owner if you can let them socialise for a while, let them have a sniff but totally ignore them. Talk to the owner but dont even look at the dogs. When he is quiet praise him vigorously. If he starts again, do it again. Try and do it with every dog you meet. With luck after a while he will get the idea. Try not to transfer your negative body language through the lead. The dog can sense it