Saint Bernard Over-Protective

Question
Hi,
I'm a proud owner of a female almost 3 year old Saint Bernard. She
I've had another Saint in the past as well as 2 Great Danes, and this is the first time I've ever had a problem like this.
   Around her first birthday, my Saint has been showing signs of aggression. However, it is never directed towards me, my four
children, or any of our cats or other dog. It is more of a protective aggression, snapping or growling at visitors. It has gotten most problematic in recent months, and i cannot understand why. We have a select few people outside of our immediate family who she knows and loves, but besides that she will snap/growl and anyone else. Especially males. She is particularly watchful of my youngest daughter and myself, and shows the most aggression when someone approaches us.
  To correct her behavior, we use no verbal communication, and simply push her back with our legs, away from the person until she sits. This helps calm her down, but unfortunately we do not feel comfortable enough to let her free with company, and usually confine her to one section of the house until they leave.
  She gets plenty of exercise, and is a sweet, lovable well behaved girl around her family. I would really just love to be able to share her with the world.
  Do you have any advice on how to her calm her down, and make her realize that people aren't so terrible?
Thanks so much

Answer
This can become a very serious and dangerous situation and does have to taken seriously,as well. The best thing you can do is to call different dog trainers and explain the situation and find one that can come to your house and see what is going on. A trainer is the best way to go,as he or she can see the behavior and find the best way to correct it.