A great way to thwart hiring-bias lawsuits: Retain all your notes from interviews.

Sometimes, you'll be lucky enough to have several qualified candidates for a promotion. The only downside: Someone who is well-qualified will be disappointed not to be chosen--and may suspect a discriminatory reason.

Protect against failure-to-promote lawsuits by following a few common-sense rules. Ask every candidate the same questions, noting their responses in writing and any quality rating that you make for each response. Retain those notes for at least three years. If a group of managers interviews candidates, collect and keep notes from each panel member.

Recent case: Amee was a veteran police officer. When a particularly desirable promotion opportunity opened, Amee applied using an online system that screened for minimum qualifications. She made the list of 19 individuals chosen to interview.

The interview team asked a standard set of questions for each candidate, noting their...