Protecting my source code

I have developed a number of apps in php that I put out with customers. I'd like to be able to retain my intellectual property on my code but there is really no way to protect it as the pages are basically source code. Does anyone know of a way to protect php source in this situation? Something like the crypt function that cold fusion uses would be ideal, this give cold fusion programmers the ability to encrypt their source and the server understands how to decrypt pages at run time, so customers never get a chance to view actual source. There's definately a need for this kind of utility in php, or perhaps it's already there and I just don't know about it? Steve.