How can I stop files infected with ransomware from replacing my cloud backup?

I saw this question on Security.SE and it got me thinking about my way of backing-up my data.

The way I do it is by storing my most important data (including kind of personal things) on a folder on my hard-drive which is then synced to my Google Drive account with the help of Google's application. This enables me to both back-up my data and sync it across all my desktops/laptops, therefore making it accessible no matter which device I'm using.

But here's the problem: the syncing part is automatic and can not be disabled. This means that, if I ever for some reason get infected with ransomware, it will encrypt my files (they're technically stored on the hard-drive) and then replace them on the cloud.

My question is: how do I protect myself against this possible situation?

I thought about 2 candidate solutions:

• store the data on an exteal hard-drive as well. Maybe re-sync it with what's on the computer once every month or something like that. The problem with this is the big redudancy (copy of a copy of a copy...) and the fact that you can easily forget to re-sync them.
• if the infection does happen one day, simply get the data back from another desktop/laptop which still has the originals (by killing its inteet coection at startup). The problem with this is that you can easily find yourself in the situation when your other computers have very out-of-date files.

Are there any more effective ways of doing this?