How to preempt plagiarism accusations
It is hard, if not impossible, to pre-empt accusations of plagiarism. The key is to be prepared to defend yourself. People rediscover stuff all the time. I would make sure that you keep all of your notes, drafts and any literature searches you may have done. I think keeping them privately would be fine, but if you really wanted to, you could make them publicly available in an archival manner to demonstrate that it is really your work.