I would love to get help with my ***** she barks when the neighbours are outside?

Hi Dr Harry, my Labrador ***** named Missy barks when ever the neighbours either side of us come out into their yards. We seem to think that this stems from when she was a pup as one of the houses was empty for 5 years and an old guy from across the road used to come into the property even tho he wasn't allowed too looking for his cats but he is such a nosy type of person that he would deliberately look over our fence and tease my dogs, because of this Missy now associates every male with this gentleman and barks at male friends or workmen until she gets to know them can you help me to try and stop her from barking so much please