One of my favorite concepts is the ‘Hidden Fist’ technique from Heian two (or Heian Five, from which I borrowed the below graphic).
A technique as a concept, don’t you love it?
Anyway, the idea is to strike in such a manner that somebody doesn’t see it.
Several ways of doing this, but, in Pinan Two (Heian Two), there is a specific technique in which the defender punches under and on the line of the attacker’s arm, thus, the attacker can’t see the counter because his own arm is in the way.
Here’s the graphic of how it works. The image is actually from Pinan Five, but it works the same.
Obviously, you’re going to have to make your body movements quick and subtle, because you don’t want him to even have a clue that you’re sneaking a punch in under his own arm.
Tell the truth, while this technique has great value, I think it is more suited to sticking a knife into the armpit of someone wearing armor, which would be more in keeping with the original Okinawan Naha-te.
If you want more in this vein, the Kang Duk Won book (part of the Evolution of a Art course) has all the forms, and the original fifty techniques that I was taught. And I was taught second generation American, so it is a tight line back to the original art form.
You should check out the Evolution of an Art course. It is three complete arts, dozens of forms and hundreds of techniques, and for one incredible price.