Prevent staff adding an extra tab
 

Hi All
My question is simple I hope.

We use Excel as a staff timesheet, the staff record their hours on one tab and submit it to be approved.
There is a seond tab which takes the data on the first tab and converts it so that we can upload it to SAP (please no comments about SAP, I'll just cry!!).
the problem we have is that some of our staff are not capable of leaving well alone!! we have had staff add aditional tabs between the tabs we use resulting in thar staff not being paid.
Of course thats my fault !!
So the question How can I prevent staff from adding a new tab?
I have already protected the two tabs we use (already had some one break the security!).
Any help greatly appreciated.
and you can then comment about SAP.

Mark :)

Worksheet protection?
Workbook structure could be locked.