I see this posted a lot here on FR...and I know most of these comments are in jest. However, I do hope people realize you aren't going to shoot these things down.
First of all, you don't hear them...so you don't know they are there. Do you know of anyone who can hear a lawnmower from a mile and a half? Second, they fly at an operational height that will certainly prohibit anyone from shooting them down with a rifle.
There is a reason the terrorists hate these things so much. There is no defense, available to the average man, against them.