invincible is to strong a word,like all techniques' it relies on you having certain atributes, certainly a strong grip is a strict requirement, both to shut off the air supply and to resist them pulling it off. It isnt to squeeze the wind pipe rather to force your fingers round it so you have a large round object( Adams apple) in your hand. That makes it difficult to remove as you have a good degree of purchase. You only need to hang on for about 20 seconds before they start to pass out. So it then dependent on what both they and you are doing with you hands. Their life preserving instinct with be to use both hand to pull your hand off. If they instead manage to over ride that and say start punching you. Then it become a case of taking what they can throw till the lack of air takes , you of course have a free hand to throw you own punches, / block or whatever