Use your hosts file, if you are using windows 7 you can find it here:
Open it with notepad you will have to select notepad from the list of programs. Scroll all the way to the bottom and add this entry without a comment (#)
127.0.0.1 Welcome to Facebook - Log In, Sign Up or Learn More
That will route whomever is trying to visit facebook back to your local system. I had to do it once because my ex was spending twelve hours/day on facebook. Then she went to AIM and I had to add entries for aim. Yahoo, lol all of the above. Then, after you save the file right click on it and hide it.