100% protection from the ordinary physical damage interrupts. kneeling, moving (including forced movement) and obviously dieing wil still stop you. skill rating effects duration, though duration in this sense is a bit misleading.

the best analogy i can give you is seigan+third eye. while you have it it WILL work 100% of the time for the things it blocks, but you might just lose it after any instance.

enhancing skill is believed to make losing it less likely