Seems possible that if you work in an environment where you have to worry about a mentally ill person potentially grabbing your knife, then you shouldn't be carrying one around. At least not carrying it around in a manner that would allow someone to grab it. What about having the knife attached to a stout lanyard that's attached to his belt? Or maybe one of those clip-it(?) knives, I think Spyderco makes them, that have a built-in clip at one end of the knife. Clipped on the belt loop and lying in the pocket, it'd be tough for someone to grab it off you quickly. Yeah, so I guess it seems to me the solution to this problem is not a knife that locks closed, but one that is fairly securely attached to the person. Gives you more options, what with so many knives having lanyard holes, shackles and clips. Let us know what he decides on.