Ctrl + Alt + Delete is a Windows function and that would not be appropriate to disable a users computer from using their Ctrl + Alt + Delete key combo if and when needed.
You need to educate your users on how to properly exit your application. Stressing the importance of not corrupting the database [their data] would be also be wise.
You could add the steps into your application to record when a person logs into your db and when they log out. If you have any records where the user did not log out then you know that they did not "properly" close your application. Search this forum for others have posted their methods for tracking their users.
HTH