protect from whom, other developers or users on the site?
If its from the sites users then you have no problem as it is parsed by the server and not code is ever sent back to the user.
As for from other developers - welll - PHP is part of the open source gang - the clue is in the name OPEN SOURCE. If you are wishing to protect your code (say) from a client then zend encoder is the best option at the moment. No only does it encode it but it also uses zend optimizer which is a pretty nifty tool
GM