There are bound to be times when you would have to use the Home button, as the only way to recover from a situation (like, if things were locked up and you had to hold the home button and power button to hard reset the iPad). In a kiosk I programmed we put a paper clip sized hole in front of the home button. That way we could turn off the gestures feature to stop people from exiting the app, and turn on kiosk mode so that anyone with a paper clip still couldn’t get out of the app without knowing the password.
There is a deactivate event, if you had gestures turned on you might be able to launch another app if the user tried to quit. Or you could have a feature in the app that after the user has entered the right password you would launch an app that didn’t require a password in order to quit.
But that all seems like a lot of effort, compared to just having a paper clip sized hole.