How to prevent disabling of apps
If you have root, you move the app to /system/priv-app; privileged system apps can't be disabled through normal user methods.

Otherwise, it's up to the application to support Device Administration.  Apps like Norton App Lock should be implementing this if they don't already, since this kind of thing is exactly what it's designed for.  Registered and activated device administrators can't be disabled or uninstalled until they are deactivated.