Beth, I don't know how skilled or brave you are at cake decorating. I personally tend to make a mess of anything complicated, so I always try to simplify. I think I would be inclined to get some of those shark-shaped gummi snacks or crackers, and put them on a cake iced with blue, to look like water. If you want to get fancier than that, try cutting a sheet of paper to the size of a 9x13 cake pan, and then free-hand a shark shape on that to make yourself a stencil. You'll end up with a roughly triangle-shaped piece cut out for the open mouth, and you can use that for his fin. I would think you could break crackers into triangles for shark teeth to line the mouth with. Or maybe you can find better ideas on the web. Anybody else have ideas?