Booby-traps. Just an idea. Didn't say it was a good one.
These kids who are my neighbors always go to my backyard whenever we tell them no. My little brothers is friends with them so that gives them confidence to come in whenever they want! How can I get them to stop coming and making a mess in my backyard?
Hire them to clean your yard & pay them something. Get them to cut grass, clean windows and such. This put you into a power mode as being their employer. A win/win situation !