[fgshepherd]

In this case, consider telling the owner - with no dogs around, of course - that you have become concerned that his dog may be able to get out of his control even on a leash and attack you and your dog. .

I think a friendly, non-judgemental approach is best. My dog IS a handful around other dogs. I'm well aware of it and I'm working very hard at getting it under control. This man and woman may be trying their best. If someone said this to me, it would make me feel very very bad.