List down some reverse Engineering Techniques for PHP to protect the code and provide security to large applications & websites?

There are several ways but so far none of those defeat security risk E.g. obfuscation, encryption like Zend Guard and/or Ioncube...but at the end of the day, zero day exploit will always be available. So the best way way typically is just to follow secure standard practices like OWASP, SANS and other security guide besides even in underground sites the single and most important lesson is to have a server or PC not connected to any network.  c",)