For your programming language, try to come up with a piece of code, that, no matter what is put around it after the fact, cannot be compiled/interpreted.
Code... Your snippet ...More Code
Shouldn't be fixable by doing something like this:
Code... # Multiline Comment Start Your snippet # Multiline Comment End ...More Code
So your snippet's codeblock itself won't be touched, but everything around it can be tweaked to try to ignore it or make it work somehow.
Your task is to come put with the shortest possible block of code(number of characters), that cannot be part of any compilable/interpretable program of your language.