I use an all-in-one security app-LEO Privacy. It has many features.

AppLock: Lock Everything - Lock up your Facebook, Whatsapp, Messenger and other important apps which may leak your privacy. - Nobody can open locked apps without entering the right password. - Pin code or pattern lock, two types of password with interesting applock theme. - Delicate themes to decorate your applock screen - Customize your lock mode, lock different apps under different circumstances. 

What's more, LEO Privacy can automatically and intelligently lock apps by time or location. It helps us hide everything.