My suggestion is to do what you would do with any other crime in progress. Whip out the phone, record them, continue to call CPD and when everyone has had enough of being told their cans are not private property, submit a petition, complete with video links to the city, DEMANDING increased litter enforcement in the community. There is a fine of up to $500 for littering. Ask yourself WHEN have you EVER heard of anyone being charged and paying that fine? They have no problem sending code enforcement out here for YOUR money, let them take some cash from the bad guys.