At that price, they're not just called "guard dogs" but "executive protection dogs". Harrison Prather owns a South Carolina-based company that specializes in training elite protection dogs for private individuals. Julia, a German Shepherd that cost $230,000, helps protect the family of John Johnson:

Mr. Johnson said he got his first protection dog after receiving personal threats while he was running the Northland Group, a debt-collection company in Minnesota that he founded and eventually sold three years ago. Now he has six protection dogs, all German shepherds, and normally takes a couple in his car whenever he goes out.

“It’s for both security and companionship,” he said as Julia nuzzled his leg, looking like a gentle enough companion. But when an intruder emerged near the tennis court of his estate, all it took was one command, “Packen!” (the bite command from the German word for “seize”), to send Julia racing across the lawn.

She sunk her teeth into the intruder’s arm, which was encased in padding for a demonstration, and hung on even as he lifted her off the ground in a vain attempt to shake free of her. She let go only upon being commanded and then stood guard over her new prisoner, barking and threatening to bite again whenever he made a move to escape, which he wisely did not try.

Link -via Glenn Reynolds | Photo: Allen Brisson-Smith for The New York Times