When I lived in Europe, I had adjustable leather leashes for the dogs. They were regular leather, but didn't have a fixed size 'handle' on them. Instead, they had a clip on either end, and several rings along the leash, to which you could clip the handle part so that the leash would be longer or shorter, depending on what you wanted/ were doing.
Here is a link to an image of such a leash (shown with 4 identical leashes, in their 4 varying settings)
link to leash image
Has anyone seen such a leash in Canada? If so, could you tell me where? I've looked at a few pet stores here, including higher end pet stores, and none of the staff seem to have heard of them.