good show Joerng, the back of the knee is the best method I have used. The one hand grip is good but usually only works strong side, most can't get that one off side. I have trouble using offside onehanded but the knee works both sides. No matter how it is done there will be some sort of grip change assuming the other hand has been injured in the fight. having a weapon with ambidextrous operating mechanism is also a good idea.
Gun control is hitting what you are shooting at.