For a long time now, I have been writing fan fictions based off of the storyline of a board game. I have posted these fan fictions on a website dedicated to the same board game. I am not the only writer doing so.
However, the time will come when I want to publish a real book, and I am finding that my inspiration is flowing from my fan fictions. This is not a problem, as most of them are very removed from the board game. With a little tweaking, I can separate them entirely.
My problem is this: Though I trust my readers, my fan fictions are on the internet, where anyone can walk by and grab them. I have attempted to thwart this by making them PDFs with the copying and printing turned off - but my proofreader can copy and print them just fine.
How can I secure my unofficial fan fictions against plagiarism? The website they are posted on does claim everything on it as copyrighted, but I would like to be doubly sure. If it comes to it, I will have to simply delete the fan fictions. I may have to do so anyway if I begin publishing.
Note: My problem is NOT with copyright. I am drawing only inspiration from these fan fictions, not actual aspects of the game. I want to be sure the plot of my fan fictions cannot be stolen, as they will be similar (similar, not exact) to the published work.
P.S. To be clear: I am not a published author, and these are not fan fictions based off of another author's work. They are based off of a board game storyline. Many others are writing similar fan fictions as well, so it is not a question of getting into trouble with the owners of the game (which is discontinued anyway).