I actually never heard of Foursquare until just now, but if someone is using that, it seems to me they WANT people to know where they are. The purpose of wanting people to know where you are is so they can possibly come to meet you. If you have a smartphone, you can already access a person's Facebook profile. If you don't want to be found, don't fuck with Foursquare, and stop posting your location on FB.
"The best kind of pride is that which compels a man to do his best when no one is watching."