Moguls and celebrities now routinely pay $40,000 to $60,000 for a well-bred German shepherd that is certified as an expert in the sport of Schutzhund, which means “protection dog."

“When you compare the costs of a full-time bodyguard versus a dog, the dog makes a lot of sense,” Mr. Curry said. “And the dog, unlike the bodyguard, can’t be bought off.”