been a solid technical solution to protect you against the act of copying software, not for Perl programs and not for any other language I have come across. Only copyright legal protection and licences can help you out if you really need it.
To ensure that your authorship is beyond any doubts in fact the best approach is to publish your programs, hacks etc. as early and as widely as possible.
Rather than having people pay a licence fee for your software, consider to ask people to contribute for actual software development- and software maintenance services that you agree to provide to them. And remember if it were not for that vast Perl developer community you yourselves would have no option to benefit from the collective knowledge and Perl software module base that exists today.
So once you completed a really excellent module why wouldn't you consider it your turn to contribute?