I wonder how long it will be until a specific anti-drone gun is invented. Seems like there will be a strong market for one soon.
Perhaps someone else can identify it, but from it's specs, it looks like it can probably fly reasonably high... if it can manage 6-8 hours at 400km range, it looks like it kind of slots in somewhat below http://en.wikipedia.org/wiki/ScanEagle in terms of performance (and cost).
From that guess, I'm thinking that this sucker is flying well over a mile high, which makes most gun approaches (unless they brought in a whole anti-aircraft platform...) pretty unfeasible. In any case, the cost of shooting down one of these would be pretty high - you would almost certainly need a weapon with guidance somehow (ie, a missile, which is going to really cut into your profit margins), extreme luck and patience, or lug around anti-aircraft platforms... which might not actually be out of the picture.
One of the things this article doesn't really tap into is how the nature of the poachers themselves are changing. The poachers themselves are becoming more militarized (as are the wardens now), partly due to the hilarious amounts of money poaching generates - it apparently, they represent a significant revenue stream for various African Paramilitary groups. http://motherboard.vice.com/blog/rhino-horn-crisis-and-the-d...
In any case, like most illict trades, constraining the supply rarely makes the problem go away - you gotta shutdown the demand somehow.
That "If you can see or hear that drone" probably is where the problem lies, but that might be solved by having your drone listen for the distinctive hum of the drone's engines. That way, you don't have to be able to continuously see that drone from the ground. Just launch your own drone; if it hears another drone, it will home in on it.
Alternatively, I would try jamming the drone's signals or taking over its controls.
In any case, such an attack is unlikely to work. The crash into the ground is least likely to work since most drones will likely have an independent altitude information. The stall method may work - if the drone has no INS and the operator is asleep.
US influence extends further.
For example, Boumediene v. Bush establishes that the US has "complete jurisdiction and control" over Guantanamo Bay Naval Base, even though Cuba retains ultimate sovereignty. And US jurisdiction in parts of Antarctica is .. complicated. http://219mag.com/2011/03/23/u-s-government-fails-to-protect... .