She/he will probably scare the bad people away wither her/his bark but if they saw her/him then no probably not. Dogs act different when there owners are not home. They are doing there job. I was a breeder of Golden Retrievers and love them dearly but they are not without fault. My dogs were protective of their yard but when out they were nice and I would even worry someone would steel them. I did have one that was very mean and he had to be put down. It hurt but it was what had to be done. I raised Springer Spaniels and they also were not without fault. Springers are very aggressive. I own a Pit Bull now and she has been the smartest and most docile Dog I have ever owned. I have had many many dogs, small, medium and large and have loved them all. People don’t understand that when dogs run with other dogs chances are high that something bad is going to happen. People don’t understand that when something (Person, Cat, Dog, ect...) the dog or dogs will chase and most likely hurt what ever they are chasing. If a dog is aggressive, don’t move and nine times out of ten the dog will go away or you can use your phone and call for help.