Enter the code for the permissive action link incorrectly a few consecutive times and the device is rendered non functional. It would take a complete reassembly.
How can we be sure they either do not know the codes, or have the knowledge to dismantle and reassemble?
....they should enter the codes 1 less than the maximum today. We can always ship "dead" nukes back to Pantex who can get them up an running in a couple of months. I'd rather have 50-60 nukes deadlined than ISIS get ahold of one plutonium core.