You could make it ping a server of yours, and if it doesn't ping after some amount of time you ask them about it. If you are "physically" giving them the code there's no way to guarantee they won't do anything to it, obfuscated or not. So you could add ways to track customers and then add repercussions in the sale agreement for removing it.
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You could make it ping a server of yours, and if it doesn't ping after some amount of time you ask them about it. If you are "physically" giving them the code there's no way to guarantee they won't do anything to it, obfuscated or not. So you could add ways to track customers and then add repercussions in the sale agreement for removing it.