Redundant hard drives.
Look into RAID arrays... they can be set up to keep multiple copies of the same data on several physical disks, completely transparent to the operating system. You work and save as usual, and the backups are automatic. When one disk fails, you simply replace it with a fresh one. The cheapest systems use regular hard drive controllers and are software driven. The more expensive systems offer more options and better performance by embedding the RAID function into the controller hardware. If you want long term.. you can dump your disks to tape every once in a while, and store the tapes somewhere else. Tape systems are generally expensive and slow but the media is then separate from the read mechanism, meaning you don't need to depend on some 10 year old hard disk you stashed still being able to spin up. You can put a really old tape into a reliably functioning machine. Tape is also a less dense (bits/unit surface area) medium than a hard disk, meaning the data will stand up to stronger interference for a longer period of time before becoming corrupted.