I'm not completely certain what you mean, but certain persons sends themselves copies (disks or cd, dvd, etc) by registered mail and then keep the envelope sealed.
It proves they have produced this work in this certain period.
Post in many forum the "Work in Progress" and in a web site can maybe a piece of evidence because there is a date and many people have seen your works ;)
And this gives you some celebrity and this is very difficult to fight ;)
Try to rip off the Nixus of Cristobal Vila http://www.etereaestudios.com/docs_html/nixus_htm/nixus_index.htm seems impossible !