I would agree that it really comes down to what you feel comfortable with,here is a list of options I see.

1) make it a public or protected function in your controller
2) put the function into a trait that you can then use anywhere you need it
3) create a BaseController that extends Controller and contains this method. then you can simply extend your BaseController (good place to put other helper functions that might be needed in other controllers, too)
4) create a global helper function that you need to register in your autoloading
5) listen to the creating Eloquent event on the database and add your logic there