If you right-click the project name, and select Properties, Lock project for viewing (you must enter a password), and close the file, you'll need to password to view the code again. I bet somebody has a crack out there for it, though, so take it with a grain of salt. Hope that helps!
VBA Password Protection is much more robust than Excel. To whit, unless you're a ******* by nature, you'll need a commercial solution, and most users aren't going to shell out the $45+ just to see what you've got.