You shouldn't want to do that. It's evil.
If you still want to, this
Some other items on JGO answering your question, or at least, looking for answers:
By the way, what makes you want modders to not be able to mod? Likely your game won't get popular enough to be modded, anyway, so why bother? That was not meant as an insult; I'm sure the majority of people's games here will never get modded.