Ask HN: What do TS/SCI poly or NSA/xIA employees put on their resume in future?
How do you make up the 6 year gaps? Is it easy to get work afterwards? How do you explain in job interviews what you were doing?
If you're talking about tech type jobs, how detailed you can be depends. Quite a lot of tech stuff at those places is mostly not classified, it just deals with classified data. If your work is classified in itself, then they have security offices that can help you out with what you can say about it, but it's probably not going to have to be "nothing at all".
If it's really so secret that you have to pretend you weren't working there, I suppose the cover office would help you out, same as while you were working there. That's going to be a really small percentage of the total employees and contractors at those places though; very few people would have to do that.
In general you're allowed to say on a resume that you have a clearance or have done a poly. I think saying "TS/SCI" is ok, but not which SCI compartments specifically. They discourage you from polygraph details too (saying "full scope") though I've seen people do it.