IGun

Guns should have electronic chip, which would allow their use only when majority of people around approve it. Think IGun. Now if a terrorist kills a guard and gets his gun then he wont be able to use it on hostages, unless they themselves allow his gun-use by pressing "confirm" on their smartphone.

That way lone gunman and a-few-terrorists scenarios will get eliminated, but when a large group of people comes out to protest, totalitarian government wont be able to stop them from exercising their democratic rights.

Same way people would be able to hire a sheriff and give him right to police some locality, without fearing he will use the gun against to subvert democratic procedures.

What do you think?

Also, gun use could be limited to some locale. I.e. if you want to protect your house and family, then your gun use can be limited only to your house, and only when your neighbors approve that.