How in-depth is the background check? If there are discrepancies with work history, and they come to you, and you give them your records, do they accept it, or do they press for more information if they think it's fishy? Do they call supervisors to verify employment, electronic records, or just call HR departments?
Seriously, good luck. If you are this concerned there is probably something on your résumé that you fluffed up a bit. I'd update my résumé with info you don't have to worry about. They do not call supervisors, just confirm employment dates. They do this by going through available records that you will usually give permission to access. If you glossed over large gaps, they may find it. Look, we all have something on our résumé that we are either not proud of or that we inflated. When it comes to verifiable info, just be careful.