Located in several levels are red gas canisters with a small pilot light on them.
These can be pushed easily by walking into them. If you can get behind the smart 
gun, push it as close as possible and strike it once with a heavy attack (should 
be a tail strike). You will have a small amount of time to flee before it explodes,
disabling the smart gun. Note: Some smart guns will require a nearby terminal to 
be activated and some simply cannot be turned off, as they are used as a device
to herd you in a certain direction.