Here is an example of what can happen when you ask those crossing your land to stop.
Someone I know had a nice house and a large lot in a subdivision. Kids were regularly cutting across his backyard to catch the bus and he was allowing them to do this until some older kids started doing things like turning over his grill, throwing pieces of trash onto his lawn, etc. He stood outside one morning and stopped each person about to cut through and politely explained to them why they could no longer use his yard. That night, while he was in bed, someone, probably the offended hoodlums threw several molatave cocktails against the side of his house and burned it to the ground. The owners did manage to get out safely.
Oh my goodness—the stories are getting worse and worse.