[c-five]

I think it is even simpler than that. I think the astronauts left laser corner reflectors at each of the landing sites. Unless some kind of dust adheres to the mirrors, they should still work. Just zap them from the surface and watch them blink back.

[c-five]

http://sunearth.gsfc.nasa.gov/eclipse/SEhelp/ApolloLaser.html

Yep, here you go!