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?

These control-the-guns schemes has one fatal flaw: you can actually make your own guns without smart-tech. All you need is getting metal pipes of sufficient durability and size. You can even build your own tank - a tank is an armored car essentially(that what US troops were doing with their military vehicles in Iraq, welding plates and stuff).