Screw ups in TTT

Didn't you think that a many things should have been left the way they were? A couple parts of this movie just didn't settle right in Middle Earth. In a previous topic, I talked about Aragorn's fall over the cliff. In this discussion I was curious if anyone else "smelled a little foul" in The Two Towers. One such scene was the one in which Frodo and the Nazgul come face to face. To me, this could be Jackson's biggest mistake of the films. If the Nazgul saw Frodo so closely to Mordor, don't you think that Sauron would be told? And if this happened, don't you think that Sauron would have some sort of guard around Mount Doom?