My almost 2 year old, female yellow lab got fixed shortly after she turned 1 year old. Since then, she seems to bark and growl anytime a man comes over to our house. She does this with men she has never met before, but also ones that she knew prior to her surgery. She is comfortable with some men but most men who come to our house, she now growls at. A little more info- I moved from a farm where she could run around with my other dog to a small town where she now stays inside while my boyfriend (who the dog loves) and I are at work and she is now the only dog in the house. What can I do to help her?