>> Because the planet’s atmosphere is only about 1% as dense as Earth’s only the smallest dust grains hang in the air. It should be possible to move a few lar

>> Because the planet’s atmosphere is only about 1% as dense as Earth’s only the smallest dust grains hang in the air. It should be possible to move a few larger rocks, maybe? Spirit, Opportunity and Curiosity have robotic arms. Good image processing might or might not recognize patterns in the stones. (http://nssdc.gsfc.nasa.gov/image/planetary/mars/vikinglander2-1.jpg http://nssdc.gsfc.nasa.gov/image/planetary/mars/vikinglander... for an example what most images I saw look like. I imagine it looks like this after a storm: http://nssdc.gsfc.nasa.gov/image/planetary/mars/vikinglander1-1.jpg http://nssdc.gsfc.nasa.gov/image/planetary/mars/vikinglander...) (Of course, compared to mikeash's answer, this is overengineering and only applicable if their conditions are not met (prearranged meeting point; we have a map and know our location))