Help with security or rights management

I need to secure some workbooks so that only certain people can use them. Unfortunately it doesn't look like my organization uses Information Rights Management as we don't run a Rights Management Server.

Is there something I can add (and hide) in the workbook so that f somebody was to email the workbook to somebody else it would not work? Like some kind of function that says "if workbook isn't opened from X network location then don't work"?

I'm not dealing with National secrets or anything and the people that I'm concerned about wouldn't have high level (or even medium level) excel skills.

Any ideas to secure things other than a password? I don't want a password because that could also be shared......

Create a small text file, placed on your server. Include code in the workbook that checks for that text file first before doing anything (even opening / visible).
If the text file is located your workbook opens. If not, have code that destroys the workbook.

There are 3rd party products that will scramble your code, making it near impossible to read the code. You can include this as another method of
obscuring your code.

Keep in mind that Excel is not very secure (by design). So ... completely securing your work is not feasible ... if someone really wants to use your workbook
they'll find a way.

I like this idea very much. If I hide the file or put it in a really obscure folder this will give me the security level I need. Thanks. I'll search for a way to do that.