Reader concerned about wandering pitbull

I am really upset with our dog catcher. I have been having problems with a stray pitbull for three weeks already, and having my neighbor dogs invaded my fenced yard. I have a chihuahua, a 7-year-old child, and I am six months pregnant. The neighbor dogs are aggressive, and the stray dog is trying to come into my house and growls and barks at kids walking home from school. I called the sheriff about the stray dog, and was told he could do nothing about this dog because it hasn't bit anyone. He asked me to see if the dog is aggressive, I am not going to walk up to a dog, and see if it will bite. I have not let my dog go outside to use the restroom because the dogs are jumping the fence, and getting into my back yard. I thought a dog catcher's job was to pick up wandering animals. The only way they will do anything is if the dog attacks. Wouldn't you want to prevent that? I have been keeping my dog contained. I have a fenced yard for my dog, and I can't even use it. What am I suppose to do about this problem if the sheriff won't help me?