Open Finder
Click Go in the menu bar
Select Recent Folders
Right-click the folder you want to protect
Choose Get Info
In the Info window, click the lock icon if available
Enter your administrator password
Check Locked
Close the Info window
If Locked is not available, move the folder to a protected location
Use FileVault to encrypt the disk
Use a password-protected disk image for the folder
Use a third-party folder-locking app if needed