We watched as the rats ran along wires between two handlers. When they smell a landmine, they stop, sniff the ground and begin to dig. This signal lets the Apopo staff know they have found a mine or some other explosive, which can then be removed.
Rats, according to Apopo, are much faster than men using metal detectors and are not distracted by metal contaminants. They are much cheaper to maintain than dogs and are easily passed between different handlers.
I did a bit more research. The rats do seem to be quite effective at clearing land mines, and this organization it noted for being efficient and well-run. They need more money for research and rat training.
You can pay to sponsor a rat. I have done so.