The Defense Advanced Research Projects Agency, which in the past has funded such experimental projects as ARPAnet (an experimental computer network that was later renamed the Internet) is currently funding a project called the "Self-Healing Mine Field."
The basic premise is this: An army lays down a field of antitank mines. The mines all communicate with each other, and have the ability to move. If someone clears a path through the minefield, the mines react by automatically rearranging themselves so the path is closed.
And you though people had trouble clearing out minefields left behind from long-forgotten wars now.
There's a Flash animation about the project that you have to see to believe here.