The only absolute security is found in second backups. Since I regard online backup as less than satisfactory -- some have reported bad experiences when trying to restore -- the answer would be a second backup to a second external drive which would be then moved to another building. This drive might be updated every two or three days, insuring minimum data loss should total disaster occur. The latest two or three days of the primary data sources would also need protection.
But Rebit will not allow this. It works with only one drive. Granted it is great for casual backup -- I really do like this cutting edge product -- but for professional grade protection in depth of data that must never be lost in the worst case scenario, I can't use it. I don't like have two seperate backup systems for different machines, but that's how it is. Rebit is too good to pass up for non-critical machines, but not good enough for the most important stuff.