Are Border Terriers good guard dogs?

No, Border Terriers are not good guard dogs. They are friendly, sociable, and generally non-aggressive dogs. While they may alert their parents to the presence of strangers with barking, they aren’t protective in the same way breeds specifically bred for guarding purposes are. Border Terriers are more likely to greet strangers with curiosity and friendliness rather than suspicion or aggression. Every dog is an individual, though, so there may be exceptions to this generalization.