The protecting does not make any sense because who want to steal will steal it anyway and protecting measures will only inconvenience legitimate, law-abiding customers.
You could try BCompiler. We have been using that for some time now and it works quite fine, however keep in mind that it is experimental and will incur some limitations whatsoever.
NuSphere has a product called NuCoder that is supposed to encrypt and convert your PHP code to bytecode. It’s at www(dot)nusphere(dot)com if you want to see the description.
I use two of their other products and they’re good, and the company is responsive to inquiries as well.