Hey Brown
Firstly, I get the feeling I may have offended you. That was not my intention, and if I did, I sincerely apologise.
I do understand where your coming from, I am Govt as well...and some of my stuff has almost gone viral in my Dept....and beacuse my name is on it, I get people, I don't even know ringing me up and wanting code changes, "it doesn't do what I want", etc.
Making things secure, as you now realise, in Excel, is extremely difficult.
As mentioned earlier, consider using
1. An Excel compiler ( easily found on Google)
2. Making the worksheets into templates, so the file will be an .xlt rather than say, a .xls
3. making the project an Addin, so it has to be installed into Excel rather than simply opened as a workbook, and has a .xla file extension.
Other posters may be able to explain these in a quick post, but I think you would be better advised to Google them and have a detailed read on how they work and which might suit your needs.