One of the reasons secrets leak IRL is that people just have to tell someone, anyone, about their secret. Keeping secrets, especially secrets that show how clever, connected or special you are, is hard.
Doing it for 5 years
Well, lately my character cracked a bit and allowed to leak some information about her, but the most funniest, humiliating and 'clever, capable and special' secrets remained secret. Although I made it possible so she can be eventually 'cracked', I put some very hard barriers against it. Some people (I wont' show finger, or they will find this character and try again haha) tried, without success of course
Sometimes I think about summarizing information that was known already about characters, but actually I would prefer to other players to find it out themselves than reading again from somewhere