If it’s original, you can register the copyright (in the US). A registered copyright means that if somebody infringed, and you sue them in court, they’re liable for statutory damages (unless you can prove it’s even more) – that’s the $150k/infringement that the RIAA/MPAA like to quote. But, to sue, you’re talking about getting a real lawyer (disclaimer: I am not a lawyer nor do I pretend to be on TV nor did I spend last night at a Holiday Inn Express.)
That’s where the DMCA is suppose to be helpful, stopping the infringement as it’s happening. Because, technically on the computer level, you can’t truly stop it from happening, not w/o withholding your story from publication. Of course, sites like AFF and others may take measures to make it more difficult, but you can’t eliminate the risk, because at some point, the reader has to be able to read it.