Okay I'm speaking speculatively and opinionated here, this is just what I was thinking, by nature full of arguable assertions.
If you know there are UAVs operating and you know where, and you have a national infrastructure intact, and you have a strategic defence system array (ie. ex-soviet states), you can flood the area with enough plain wattage to toss a wild card into the whole deal. The staff of Desert Storm did a report that got published on a conspiracy site at one point funnily enough, probably find it at wikileaks now it got reclassified when stealth systems were labelled US national security. I can't find it at the old links anymore. Still it discussed experimental (at the time) military technologies like the F-117 and UAV in operations and commented on their potential faults. Interestingly the NightHawk can be tracked actively by any civilian mobile tower network, one finding in the report of them operating over Baghdad. You have to know a rough mission routé but if you do you can track gaps in coverage moving along a flight path at service control centres, and conceivable datalink military to it (the report suggested the Russians probably had such a system in place because their strategic network is set up perfectly to achieve it).
I imagine similar approach to effectively dealing with UAVs, which I imagine small nations with modern civilian infrastructure and well equipped small military maybe capable of achieving at least to local threats. What I'm saying is, for example their weakness is that they are signal dependent.