You could possible compile some of your code, which would mean he'd need to reverse engineer it. But in all honesty this kind of thinking is not going to get you very far in the perl community. How many other people do you see selling perl libraries? And if there was any kind of demand for the thing you were creating, it would be on CPAN already. Even if it isn't, there's enough of a DIY ethic around here that somebody else will quickly duplicate your work.
in reply to How can you protect your Perl Mods/Hacks?