Why yell at them to get off your lawn when you can have a device do it for you:

The device, called the Mosquito ("It's small and annoying," [inventor] Stapleton said), emits a high-frequency pulsing sound that, he says, can be heard by most people younger than 20 and almost no one older than 30. The sound is designed to so irritate young people that after several minutes, they cannot stand it and go away.

Finally something that will keep Nina off the computer when we visit New York!