Discrimination and retaliation claims can be eliminated with independent HR investigations. That is, they can if your investigation is independent enough.
In Staub v. Proctor Hospital, the US Supreme Court ruled an HR investigation wasn't deep enough. The ex-employee's allegedly biased supervisor went to HR looking for a termination approval. The HR manager looked at the ex-employee's file which had several prior written warnings, then terminated the ex-employee.
The Court faulted the HR manager for relying on information supplied by the supervisor. Had HR gone back and interviewed everyone herself, the Court would have dumped the ex-employee's claim. That's what an independent investigation takes—face time with folks who know what happened.
Gold standard is for your HR to do a truly independent investigation on all significant employment decisions, like a termination. But that can be time-consuming and expensive. Imagine going back to interview the employee, supervisor and maybe even co-workers on all terminations. You might not need to go that far.
Also, consider doing an independent investigation on high-risk decisions. Now, you're looking at employees who have reported discrimination, harassment or overtime pay problems. Don't forget employees who recently had an on-the-job injury or filed for workers' comp.
Even if your HR investigation doesn't entirely cut off liability, it can go a long way in front of a jury. Jurors like to know that you at least tried to do the right thing. And other fundamental HR practices can still help you put the claim in the wastebasket.