Encrypt your data backups.

Store the certificates used to encrypt your backups somewhere else but equally secure.

Limit access to both the certificates and the backups to a tightly and formally designed audience.

Legal barriers? I'm sure any lawyers wondering how they're going to pay for the 3rd mistresses BMW convertible will be delighted by that. The problem with legal redress is that it happens AFTER the offence. It's no comfort to know that my murderer will get hung, I'm still dead even though it will stop the swine reoffending!

People commit crimes for a number of reasons but factored into it is the belief that they can get away with it. Albert Pierrepoint (often referred to as Britains last hangman) had to hang someone who was a member of his social circle. His comment was that the guys still comitted the crime even knowing who Albert was and what he did, thus calling into question the infallibility of a detterent punishment.