Or, back up to tape, and regularly (at least once a week) take a full backup tape out of the machine and put it in a safe offsite location.
"Old fashioned" I know, but it works. No-one is going to hack or encrypt a tape that's not in a machine. And if the office is destroyed by fire or natural disaster, you have a backup.
Fancy backup-to-disk tech is great for when someone accidentally deletes a file, but they don't help with ransomware or other major disasters.