I am designing a magazine as a contractor. How do I protect the intellectual property rights of the design?

I am worried that my client may take the design and shop it to other agencies to get a lower bid.

I am designing a magazine as a contractor. How do I protect the intellectual property rights of the design?
With all my spec work, I put my watermark over the design itself. Also, keep meticulous records of when documents were created. You can also add the tagline on the bottom of all documents CCL - All Rights Reserved - your name - 2008.
Reply:Before you do anything for the public make a complete draft and mail it to yourself. be sure you include times and dates. even the time you were commisioned to do this project.
Reply:Patent your design. It is fairly inexpensive and the whole point of a patent is to protect intellectual property.