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The Atlanta Journal-Constitution has a piece on a local bar owner who took fending off bums into his own hands:

Rufus Terrill, who owns a bar in downtown Atlanta called O'Terrill's, has grown weary of the drug dealers and vagrants he says frequent the neighborhood. Rather than put the police on speed dial or hire private security guards, Terrill has created his own private one robot security squad to keep the undesirable elements away.

The unnamed robot, affectionately referred to as either Robo-Cop or Bum-Bot by those who have seen it in action, is a hodge podge of off-the-shelf parts controlled by Terrill and a remote control. The four-foot tall, 300-pound body consists of an old smoker mounted atop an electric scooter. He's mounted a spot light, infrared camera, loud speaker, and water cannon inside the chassis, then wrapped the whole thing in rubber and painted it a menacing black.

Terrill sends the bot to the neighboring daycare center while he remains safely positioned up the block. Using a walkie-talkie, he instructs "suspects" to leave and informs them they are trespassing. If they refuse to leave, the bot then lets loose with the water cannon.

Remember, kids, unprovoked water cannon use can be considered assault - [via] Link.