Using two different drives with Time Machine
Solution 1:
You can have Time Machine backup to several drives, it will rotate among all configured and mounted drives. Two caveats
- if you disconnect a backup drive, Time Machine will alert you the next time it‘s up for backup
- If you disconnect a backup drive for a week it‘s next backup most likely requires a full scan of the source drive
It might be better to keep the two drives connected all the time and do alternating disk image backups to two other drives (and store those offsite).