I'd be careful with this. When I lived in Boston I usually had 2-3 knives on me at any given time. I'd been attacked or threatened with knives, bricks, mace, batons, etc and knives with blades under 4" (i think that was the limit) were the only legal form of protection that didn't require a license (yes, even mace requiers a permit...its freakin MA).
When I moved back to Ohio I did a bit of research on knife carry and found a VERY vague code. What I gleaned from it was that knife carry in Ohio is permitted only if it is not to be used as a deadly weapon. Also illegal are switchblades, butterfly knives, and springblades. So if you are concealing a knife, it is considered a utility knife and that is legal. The minute you use it, even in self defense, against another person, you are considered to have been in unlawful possession of a concealed deadly weapon.