Never posted on here before, but i'm pretty sure i've found the way to get the persistent perk that lets you lose only one perk when you go down. Dont know really what to call it, buts its sorta like Tombstone so i'll just call it Perma Tombstone.
Anyways. Im pretty sure the way to Perma Tombstone is to buy 4 perks before round 5, as this is how I got it. I dont have any proof that this is 100% the way to get it and the game I got it in is no longer in my recents. A few seconds after I bought my 4th perk though, I got a green poof and the next time I went down and got revived I only lost one perk.
According to this video: http://m.youtube.com/#/watch?v=zvwMD8n1 ... vwMD8n122w the way I said actually is the way to get it.