Suppose you have to put some php code in the customer server and make it working, and you want to protect it from not-authorized copy by the customer or anybody else has full access to that server. How to do it? Consider the open-source compliancy temporary suspended...
Well, the easiest way is to use Zend's Zend Encoder.
However, it's not free. I think there is a trial though.
Yes, it's also the most costly. What do you think about ionCube? Do you know other?
Please, if you're interested in Zend business, let me know.