I wouldn't say that knives are as a rule non-lethal, nor would I say that their use is always lethal in outcome.

I try to never be without some form of legal knife though how I carry changes.

What I try to get is something that will be useful in everyday situations (cutting open packages, cutting string, etc.) and can be used for SD if I have to. The fact that I use it for non-SD uses means that a lawyer is going to have a tough time declaring that I sought to use it against someone.

To this end lock-bladed folding knives are basically what I carry. I prefer those I can open one-handed. Currently a Camillus Sizzle is what gets to ride with me. It's small enough that I can carry it anywhere but on an airplane or into a jail/court. It's large enough that it can make a close situation go badly for someone who wants to be that close to me.