I have a small wallet sized external drive that I keep in my safety deposit at the bank. Every couple of months, I go to the bank and switch it with my other external drive which has a more recent backup. Then I take the other external drive home. By having two external drives, I can avoid having to make an extra trip back to the bank, each time.
I also have a slightly larger sized external drive that I keep at home for doing more frequent backups. The other smaller wallet sized external drive in my safety deposit box, is my off site backup. There is always the slight chance that the external drive at home could be lost through a burglary or fire. I use a total of three different external drives for doing the regular backups on my home computer.
On my Linux desktop computer at home, I use the rsync command to regularly update the backups on each of my three external drives.
Another off site option that I have considered, is keeping an encrypted backup on an external drive at a nearby older relatives house.