How do I stop people from cheating on my Cody chalenges?

I wrote a Cody problem, but I want to prevent people from using tricks to get a false "best" solution.

For example, many people do something like the following:

regexp '' '(?@"CODE HERE)';

in order to get the size of their program down to something quite small. I want to prevent this. I have seen people using some weird tests to try to block this, but I don't know how they work and when I try to copy them they fail.

[per isakson]

Does this count as weird?

str = fileread( which(mfilename) );
assert( isempty( regexp( 'str', 'regexp' ) ) )

btw: I don't know if works on the Cody-server