We talk a lot about, which keeps information safe from local issues like fire, flood or theft.
One extra layer of protection worth thinking about is to keep one big, not-so-regular backup, completely off the grid. This is a backup you don't want automatically updating itself every day or week.
This backup is a good safety against the very rare possibility that a corrupt piece of data, or a strange data wipe, could spread throughout all your automatic backups, and then you may find they're all damaged beyond repair.
One occasional backup that lives outside the auto process can be that final doomsday saviour.