Just a couple of things that aren't art specific, as I do not study ninjitsu, but may add value.
#1. First rule for carrying a knife for self-defense: DON'T carry a knife for self-defense. Getting a CPL and carrying a pistol is actually safer for you legally as well as physically; if you pull a knife or a gun for self-defense, lethal force still needs to be justified for either in any state. But believe it or not, a legally concealed carry pistol is more legally acceptable then a blade used to cut someone to smitherines.
That being said, if you DO carry a knife, then your knife abides by the laws of your state, AND is for utility, fishing, hunting, wilderness survival, a part of a costume or traditional dress (scottish dirk), etc., etc., etc.....and YOU CAN PROVE that is what it is for. If you carry a knife for self-defense only (especially if it LOOKS like it is for self-defense only) then that can be looked at as premeditation if you ever have to use it on someone, and it ends up in court. Observe the Preen-Wilson case for a recent example if you don't agree, however, remember that the law doesn't really whether or not you agree.
Good self-defense is using a little common sense and taking care of these details, nipping in the bud problems you could run into later down the line.
#2. I'd practice with your carry tool, including live cutting drills on targets, before you carry. Your traditional knifework from your style may be very good, but you need to apply that to the tool that you'll be carrying. Don sets a good example by working with the Delica and trainer.
Work out any problems you might have with Grip, etc., in the training hall rather then the street or field.
Also, you should be able to deploy your knife in a second or less even with an adrinaline dump; so practice opening those folders frequently.
#3. Carry a good quality tool, especially if it is a folder. It doesn't need to be the most expensive thing at the knifeshow, but it needs to be reliable. You won't have to worry about locks failing, blades breaking, etc., with a good quality piece of steel.
#4. For teaching: Just be clear as to WHAT your teaching and what it is for. Example: Assuming your pupils aren't military, if there is traditional/technical value, lets say, in teaching some sentry removal methods, then cool...teach em'. Don't worry too much about the psychopaths using your deadly methods (wink) for evil; hopefully you've screened them as much as you can. The reality is, the psycho's will just buy a shotgun at the nearest sporting good store if they wish to go on a spree, rather then waste their time and $$ on your class. That being said, make sure you specify what that sentry removal method is for, and that you specify that it IS NOT for self-defense. It may have value, as a lot of impractical things in martial arts have value (hence the "art" part of "martial art"). But don't have your students leaving your class thinking that that something like a sentry removal is at all practical, or that it will go over well in court as a self-defense claim.
So, in other words, if you teach knife methods from any style, ninjitsu or otherwise, go ahead and teach the traditional way as specified in your style. However, make sure you do yourself and your pupils justice by specifying the purpose of what you are teaching, and basically seperating what is prudent and appliable for self-defense in TODAYS world, and what is not. You don't want pupils walking away thinking that things like sentry removals as in my example, or that slice-em-cut-em-gut-em up stuff that exists in almost every knife art is prudent for self-defense.
Cool...hope that added too the discussion.
PJMOD
Perhaps it was a dead horse point to you, but I got a few nice comments regarding it, so perhaps it wasn't a dead horse to everyone and was worth elaborating on. Anyways, we're in agreement. Nice link to Macyoung's site, btw... :ultracool 
