Accessing My Spreadsheet - Password? Hide? Very Hide?

Friends, I am having an issue with someone who links to my reports I generate for an area. They have built links into their sheets that link to mine and they then use the data I produce to create their own data sets. Since I have a good idea of their abilities I do not feel comfortable with their manipulation of my data. On top of that when a VP for the area being reported on sees their data, they ask my department's representative about the data. When she sees it and knows the data I produce, it all ends back on my desk to check the validity of their numbers. So overall - they have never obtained my permission to reuse the data, never asked me to verify their numbers and possibly use the numbers in questionable ways.
I am considering putting a stop to it. Options I'm considering are...
1) Password protect the document.
2) Change the name of the sheet AND the hidden worksheets within.
3) Very hide the hidden worksheets after I change their names.
The first option would also involve changing the names of the hidden worksheets.
for #1) can i password protect only limited parts? I don't want the users to have to deal with a password, just those who try to access hidden worksheets. How to accomplish this (sorry, may sound like a rookie question but I've never password protected a doc before).
for #2) if I change the name of the report and/or the worksheets, can they use connections to simply update their sheet thus defeating the process?
for #3) if I use very hide does that break their links regardless of whether or not I change the worksheet names? Does it break the links I have in my sheet regarding my formulas? If it does not, won't they be able to see my sheet names I'm referencing in my formulas by looking at my formulas?
I'm inclined to #3 just as an FYI but not rulling out anything at this time.
Other options?
Thanks all.

I think very hidden would work as he will not be able to see or unhide the hidden sheets w/o using a macro AND knowing the sheet names. So even if he can see the sheet names in formulas I don't believe he knows the macro for unhiding them. I will have to test that out on a sample sheet. Also will test out trying to hide then password protect the hidden sheets so he can't unhide them.
Thanks Whizbang.
Anyone with other thoughts?

You can also password protect the VBAProject, which will prevent him from unhiding the sheet even if he knows enough about VBA to do it.

[Edit]

Nevermind. You can still unhide it using the Immediate Window, unless you protect the Workbook as well.