If you're asking about store it and forget it, nothing is fail proof. Accidental Overwrite is your worst enemy . . . yourself. In the end, nothing replaces proper backup procedures, so the true solution of no data loss is to get a software solution that allows it to be schedules and does not overwrite copies outside of how comfortable you are with it, and store a copy off-site.
That can't be emphasized enough. RAID is not backup. It's protection from hardware failure.
I would use all the following data protection strategies that you can afford:
- RAID: Protection against hardware faults. Sunk cost that I would consider mandatory.
- Snapshots: Near instant recovery of human "Oops". Virtually free (performance and cost) on any decent NAS.
- Local Backup: Quick recovery from major failures. Costs media (drives or tape), and time to manage.
- Offsite Backup: Slow recovery from catastrophic failures (e.g., house burns down). Can be a second copy of your local backups that rotate offsite, or an online service (dropbox, amazon s3, etc.). If it's physical media, there are professional services that will come an pick up your backups every week, or you can just put them at a friends house, preferably outside of range of a single tornado/hurricane/earthquake/flood/godzilla.
Remember, just like you only have to brush the teeth you want to keep; you only have to backup the bits you want to keep.