Leerburg police leash (for dogs), although the one they sell now is (of course) a crappier version of the one I’ve owned for 10 years now. It’s a leash with a snap at both ends, and three o rings at different points along the length to attach the top snap. It can be held like a regular leash, or slung over your shoulder if you’re for example at an outdoor eating place. I keep it on the shortest length while on walks on sidewalks and at the longest on parks and such. It’s so amazing I’m shocked it’s not a standard leash design you can buy in pet stores.