nexgen2

I'm aware that everything written in php can be decoded. I just want to make the job harder. What I actually need is that I store the "activation code" in my server and have my script check for that code to activate the script. That way I can deactivate the script if the user ask for the refund. I have heard ionCube or Zend guard can do those. Any suggestion? (I want my script to be self contained and don't want another script to be installed first for using my script)

I sell a webscript which is written in the php language. What I want to do is create a license for each user and limit the script installation to one domain only. Also, I want to distribute this same script as a free trial for 15 days. After that the user must upgrade. The script will call home to verify if the user has valid record in our server or not. What's the best and "hard to crack" way to distribute license in that way?