dogs have plenty of off-lead time in the park, but as others have said, a cat, fox or other stimulus can make any dog forget his manners and make him a danger to himself, traffic or others. My dog does not like being 'investigated' by other canines when on-lead and if this had happened to him it would have turned into a big fight! I do find it very arrogant of people with dogs off lead on the street- they are almost always the dogs that poo without it being picked up by owners too.