Almost anything you do to try to stop this would involve macros. And that won't
stop the really dedicated.
But something like this in the ThisWorkbook module will stop some (maybe even
most):
Option Explicit
Private Sub Workbook_BeforeSave(ByVal SaveAsUI As Boolean, Cancel As Boolean)
If SaveAsUI = True Then
MsgBox "Please don't save this"
Cancel = True
End If
End Sub
But I could use windows explorer and just copy it somewhere else.
(Or copy the cells into another workbook and save that one. Excel isn't made
for this kind of security.)