said by nunya :

You could spray them with a hose (They even have motion detector sprinklers for "deer").
Also, put on a stained "wife beater" shirt. Set up a lawn chair and drink heavily. Smoke a few pack of cigs while you're out there too. Then, when people walk by shake your fist at them and call them "whipper-snappers".
That oughtta do it.

Seriously though, I'd start with a "No Trespassing" or "Keep Off Lawn" sign. The deer sprinkler would be *extremely* entertaining - you must admit.