Having a Koi pond, a few years ago we were plagued by a ver persistant heron with a wingspan of over six feet. After trying everything to discourage it I was close to seriously considering mounting a Royal Navy Phalanx gun on the garage roof, set in automatic mode. However, as we are under the Heathrow flightpath I did not want to upset Air Traffic Control whose charges create similar sized shadows in the garden.
The RSPCB say Heron's are a protected species. Obviously none of them keep fish !
Seriously though, its not our widespead air defense sysytems that I am worried about, but the idiot activists with a chip on one shoulder and a surface to air launcher on the other who may be eying up the same high-rise locations.