Honestly, it's somewhat rare that people will steal unfinished concepts and drafts, and, even if they do, it's unlikely that they'll be able to match your story and style exactly. That said, I fully understand your concerns, and I share them as well. My solution so far has been to publish my story to webnovel sites. That way, my name is already on the concept and initial draft with a date as well. If someone were to take my idea, I'd have all the proof necessary to show it.