You might consider encrypting the story on your computer or device using a password that only you know. That way, even if someone gains access to your device, they won't be able to read the story without the password.
You could keep it in a private diary or journal and lock it away.
Well, one way to do it is to make the main character have a solitary adventure in a remote area. Or maybe have a catastrophe that scares everyone away. But this might require some careful world-building and plot development to make it believable.
You might consider not writing it down at all and just keeping it in your mind. Or, if it's something physical like a paper, store it in a locked box in a hidden place.
One option is to not post the story at all. But if you already have and want to hide it, you can delete it immediately after posting.
One way could be to keep it in a private diary with a lock.
One way to do it is to write it in a code or a language that only you understand. But that can be quite complicated. Or you could store it on a password-protected digital device and never share the password.
Well, you could write it in a language that only you know or use some sort of code. Just make sure you remember how to decode it later!
You could keep it written in a secret diary and hide the diary well.
You could password-protect it or store it in a private folder that only you have access to.
You could keep it in a private journal or password-protect it on your device. That way, only you have access.
One way could be to keep it in a private journal and lock it away.