The US Government is taking the threat of small UAVs to a whole new level. Through DARPA, they have put out an RFP to develop a system of monitoring UAVs flying at less than 1,000 feet in large cities. The phrase "persistent, wide-area surveillance of small unmanned aerial systems" sounds like a permanent or at least, long term system. Something similar but way more capable was flown over Aberdeen, MD and protected Washington, DC from missile threats until it broke free and landed in Pennsylvania a few years ago. I think this means that they will be strongly enforcing "no fly zones" in the not so distant future.
Keeping a Watchful Eye on Low-Flying Unmanned Aerial Systems in Cities
Aerial Dragnet - Federal Business Opportunities: Opportunities
Keeping a Watchful Eye on Low-Flying Unmanned Aerial Systems in Cities
Aerial Dragnet - Federal Business Opportunities: Opportunities