I had been meaning to teach obedience style scent discrimination and retrieve so that was going to be my contribution to the challenges that threw my way. However it is a little complex and now a cyclone hitting so will just go with one prepared for something else. The exercise I call Jar is just getting the dog to run to a placed or thrown treat jar and lie down next to it. It is one I now teach first night on a puppy class as a challenge to teach before the class ends. It is like using a dish for remote reward but the closed container has some advantages.
As well as teaching a down at a distance the treat jar rattle is a great attention getter in the park. Also I see this as gaining a source of focus in the park away from me I can control so one or two jars can be used for games in the park that help with off leash control by building them up on a long line first and then using the game to test off leash ears in a distracting environment.
When getting new people to do it I avoid showing them the end result with a thrown jar to stop them skipping ahead - they need to be good on the waiting for the dumb human to open the jar before adding the throw or you get a dog retrieving or eating the jar.