Hi,
You already have been told that the watermark won't prevent anything.
To add a water mark go to a graphics package and create a watermark
appropriate for the size of the pages you are printing in Excel. You can do
this in PowerPoint if you want. Save the file as a JPG. You should lighten
up the graphics in the graphics program so it looks like a watermark in Excel.
In Excel choose File, Page Setup, Headers & Footers, Custom Header, Left
section. Choose the button for inserting graphics (the second to the last
button) find the JPG file from above.