How should I deter my neighbors from filling up my garbage can every week?

Every week, my neighbors (a couple) drive down their driveway, pull into my driveway, and proceed to unload a trunk-full of garbage into my and my other neighbor’s garbage cans, then return up their driveway.

Today, I was curious what they were throwing out. I looked in my can, and discovered hundreds of patients’ medical files. Sure is a relief to know that my confidential medical files can end up in some random residential garbage can and sit on the street for anyone to pick through…

I make great effort to minimize the amount of trash I produce, and the thought of another couple producing enough trash every week to fill three cans disturbs me. I also think it is unfair that they feel entitled to encroach on others’ city-allocated bi-weekly garbage production allowance. It also peeves me to know this is paper that could be recycled, and more importantly, this is confidential paper that should be shredded and destroyed.

Do I report them to some authority? Do I leave an angry letter taped to their can demanding rent for the use of my can? Do I glue a dead fish to the lid? Or purchase offensive, life-threatening stickers to decorate the can with? What should I do?