What's the Problem With China's X Files?

If aliens can navigate the universe and come to earth, wouldn't they be able to avoid our attempts to shoot them down? We've spent a very unusual amount of time on these very things. There's an episode on there that works with UFO investigators in Italy is that we do know how to track the signatures on many of these craft. One of the things that we've learned how to do is, is spot them when they transition from our atmosphere and into the ocean or vice versa.