Here's the tip. Drives do fail - it's a fact of life. I reckon (just a guess really) that if a drive lasts a month it's probably going to be OK. So - on my new-new drive I've created a partition that's just a bit bigger than I need. I'll use this for a month or so, or until I need more space at which time I'll make it biggger. The benefit is that if my new-new drive fails next week I've contained my data to 1 TB of drive, which means that so long as the partition still exists I only have to overwrite 1x3 TB. Only!
It's also worth considering encrypting your backup drive - it may not be quite as secure as overwriting but if you encrypt as you create you should be pretty safe to just unplug and return. Happy days.