There is no object class event handler which binds the Visual Basic Editor environment within Office application suites. So the direction you thought of is irrelevant.
Since you already seem to have agreed to the knowledge that Office VBA security is practically of no value to the savvy ones, I'm not going to reiterate that fact in any other way.

It is a very old cliche in the Excel world that you can only hope to really secure your code, by using DLL and COM Add-Ins.