What's the simplest way to evade a $4.5 million armed, flying robot? Get some grass mats. Or smear your car with mud.

After hundreds of strikes over four drone-intensive years, al-Qaida is starting to pass around notes on cheap countermeasures militants can take to evade detection by the robots' sensors. The longer the militants can delay the CIA or the U.S. military from obtaining a positive identification, the thinking goes, the less likely a strike becomes. Step one: Disguise your car.

The advice comes from a xeroxed printout found in Timbuktu by the Associated Press shortly after Islamist militants fighting the French in Mali vacated the area. Taken from jihadi forums online and adapted, one recommendation for simple drone-proofing was to drape a car carrying militants with carpets so the cameras on a drone, thousands of feet up in the sky, might be fooled.

In the Malian case, fighters were using mats made of woven grass that seemed to let the car blend into the landscape. Or they were smearing their cars in layers of mud so as to actually appear like part of the road. An earlier version of the online anti-drone tips urged followers to tint their vehicle roofs with glass, so the eye in the sky would be tricked.

This ain't always going to work. Lots of Predators and Reapers have infrared cameras, so when a car below passes by, it's going to register the heat signature of the vehicle. For those, something that moves – and would appear on a screen for a ground-control station as a white streak indicating an elevated heat level – but doesn't look on a regular camera like a vehicle is probably going to attract unwelcome U.S. attention, not divert it.

But remember: Drones are built to hover, and their cameras are often taking fixed-viewpoint shots for long periods of time, or switching angles at particular intervals. A car traveling across the drone camera's field of vision will do so for a brief period of time before disappearing, so a crude disguise has merit. After all, drone vision isn't automated, so a human being watching on a screen from thousands of miles away needs to perceive that he or she is looking at a vehicle. Call it an irony of persistent surveillance.

Of course, if the CIA or the U.S. military is already on the trail of your particular car, your best bet with camouflage is to hope that the makeshift canopy can make the drone lose your trail. If not, it's going to follow you and fire on you, no matter how dirty you can get your vehicle. Still, painting your car with mud or getting it under a canopied area might have some utility for cooling the car down after turning it off, thereby making the drone sensor think you haven't been out driving.

"These are not dumb techniques. It shows that they are acting pretty astutely," an Air Force colonel told AP. And that really ought not to come as a surprise: Prolonged warfare always involves each side adapting to the other's techniques. In Iraq, insurgents learned they needed $26 worth of Radio Shack hardware to intercept unencrypted Predator video footage (a problem that still persists).

And it's not just militants drone-proofing their rides out of necessity. Law student Asher Kohn recently proposed building a "drone-proof city" using a network of citywide latticed roofs to block the surveillance – basically one big canopy, the high-end version of the grass, mud and carpet model on display here. (Even fashion designers are getting in on avoiding detection.) Maybe the next generation of drone sensors the military purchases will seek to see through grit, grime and foliage.