Prevent a Scene From Closing

Hi all,

I have a profile that opens a scene every time a select list of apps opens. The scene is a keypad. If the correct pin is entered, the scene closes. Otherwise, the scene returns the phone to the home screen. This effectively locks out everyone from certain apps on my phone unless they know my pin. This setup works very well, but it has a problem. If you press the back button while the scene is open, the scene closes, but keeps open the app I am trying to lock people out of. Is there any way to circumvent this issue? Thanks in advance.