One way to work around this problem is to obfuscate (= replace with
functionally equivalant, but much harder to understand) the VBA code
within the entire Workbook. That way, even if they get at your code,
it's much harder for them to understand it.

An open source Excel/VBA source code obfuscation Add-in is available
at:

http://invisiblebasic.sourceforge.net

Just use the Add-in's "Save Invisibly As" command before sending out
your workbook.

John