Prevent guest from reading an external hard drive

I have a USB hard drive connected to my Mac. I want it to be readable only by me, and not by the anonymous "guest" user. I right-clicked on the drive in Finder, and set the permissions like this:

I also clicked on the gear, and selected "Apply to enclosed items".

But when I log out, and log in as guest, I can still browse the files on the drive. What's going on here? I'm running Sierra 10.12.1.

Solution 1:

Why not just encrypt the drive?

https://www.howtogeek.com/184675/how-to-encrypt-your-macs-system-drive-removable-devices-and-individual-files/amp/

Encrypt Removable Devices

Mac OS X allows you to encrypt an entire drive, like a USB drive or external hard drive. The contents of the drive will be encrypted with a passphrase you choose and no one will be able to access them without that passphrase. It functions like BitLocker To Go on Enterprise editions of Windows, but it’s available to all Mac users.

To encrypt a drive, simply open the Finder and connect the drive to your Mac. Ctrl+click or right-click the drive in the Finder sidebar and select the Encrypt “Drive Name” option.

The disk will be encrypted once you enter your password of choice — be sure to use a secure one! You may have to wait several minutes for the contents of your disk to be encrypted, depending on the size of your drive and its speed.

Don’t lose your password! If you do, you won’t be able to access any files on the encrypted drive.