Found this over on Slashdot, after voting in the poll about Martina life, and loved it.

It must have life on it
The Martian Air Force has knocked down more than 50% of the explorers we've sent there.

I was a little worried when Spirit stopped signalling. It then occurred to me that if the Martian Air Force doesn't get you, the Martian Marine Corps will.. Ooo-rah! :)