Are Australian Kelpies good guard dogs?

Yes, Australian Kelpies are good guard dogs, thanks to their intelligence, loyalty, and alertness. They are naturally protective of their family and territory, and their indefatigable energy reserves make them vigilant and responsive to potential threats. 

However, it’s important to note that Australian Kelpies are primarily bred as herding dogs, so while they can alert you to potential dangers, their guarding instincts may not be as strong as breeds specifically bred for protection work. Ultimately, like any breed, an Australian Kelpie's behavior will depend on their individual temperament, training, and socialization.