To prevent copying in the future you can use 'Proguard'. It's pretty simple I actually did it today
This will obfuscate your code, basically making it un-readable and much harder to reverse engineer.
You also get the bonus of a smaller package size and a slight performance increase from inlining.
It's all documented here:Obfuscating Android Apps on Android Dev
If you think this isn't simple enough just ask an I'll make a tutorial labelled [TUT]