If you really must have guns on board...
A suggestion from a fare paying member of the public... Increase the price of a ticket by $10 or $20 or whatever amount necessary and hire professonally trained Air Marshalls for each flight...
I know that is not a perfect solution but it is a deterrent..
or better still...use the additional $$$ raised to improve security on the ground... and even better still....start to ask the question...why do we have the threat in the first place..If we ask that question, maybe we should work on that..
Maybe I am naive...but it might help..If we understand why we have the problem in the first place..