Are Collies good guard dogs?

No, Collies are not good guard dogs in the traditional sense. Although they might bark to alert their families to potential intruders or unusual activity, they are friendly and sociable in temperament. They often greet strangers with a wagging tail rather than suspicion. 

However, their loyalty and protective instincts toward their family can deter others in some situations, and their presence alone can serve as a deterrent to potential intruders.