PHP script protection against modification / copying

Question

PHP

What do you think is the best way to protect your PHP project from being copied and/or modified. Any options are being considered.

UPD.
Project in PHP 5.3

Answer 1

Zend encoder is long gone. Zend Guard is quite successfully opened (although I don’t know about its latest version).
Also, ioncube and sourceguardian are opened (only the tools for this are not in the public).

Answer 2

The best way is to activate the product on the off site and develop the project by regularly releasing updates. Then the people will be dragged along and the pirates will get tired of making diffs.

Answer 3

zend encoder?