These replies are outstanding, everyone! I seriously appreciate your insight and observations. I didn't realize when we started this how excitingly sly it could be, but I'm really looking forward to trying this in other jurisdictions when I travel (not soon, unfortunately, but oh well). In the meantime there seem to be several in my area that I can keep looking for, including those with muggle potential to be careful around.
Another question I have though is with the acronyms I've seen others use. I figured out that FTFC means First To Find Cache, but what does TFTC, TFTH, TNLN, and SL mean?