Using a Blade for Backup?

Whether you are Law Enforcement or an armed citizen do you carry a knife for backup?  Is it a folder or fixed blade?  How bad would things get before you would deploy a knife in an attempt to defend yourself? If under attack or a violent gun takeaway senario could you reach and use a blade?  

Some of those questions can't be answered with any real confidence, too many unknowns. I have always carried a folder in such a way that, at least in my mind, I could use it if my gun side was under attack.  A fixed blade would seem to be faster, not requiring  you to hold it in a certain way so you can get it open. My problem is I already have a packed duty belt and have ever found a comfortable way to carry even a compact fixed blade.  I have tried a couple of push knives and other styles and even partially concealed between my duty and garrison belt is difficult and uncomfortable. 

I'm a big Spyderco fan, these are a couple of my blades I consider defense oriented, and they are easy to carry for sure. But ease of deployment in a life or death situation is unsure at best. 

I suppose my philosophy would be; It's better to have it and not need it, than to need it and not have it.