Everybody should realize that there are no 100%, even no 50%, defence-techniques against a knife.
There are some good concepts - not more. If those really work depends on many factors.
So, if I must use a defence-technique in an obvious knife threat or a knife attack, there failed already before a lot of things that are important for me.
Those things are:
1. Do I have the possibility to escape?
2. Do I have something with me or is there anything lying around that I can apply against the knife or use to keep the attacker at distance?
Here is a little test for our instructor aspirants:
The aspirants didn´t know what to expect.
Krav Maga Street Defence
www.krav-maga-essen.de