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 in a password-protected file or app. That way, only you know how to access it.
Well, one way to do it is to focus on other characters and events, giving very little attention or no space to the person you want to hide. Maybe even create distractions or new plotlines to draw the reader's focus away. Another option is to have them in the background but not have them play any significant role or have any dialogue.
One way could be to simply not mention them at all. Just pretend they don't exist in your narrative.
Well, one way is to not talk about it at all when that person is around. Another option is to store it in a place where they're unlikely to look, like a hidden digital folder or a locked physical journal.
One way is to not tell anyone about it and keep it to yourself. You could also store it in a private online account that only you have access to.
You could make it private and only share it with those you trust. That way, it's hidden from the public.
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.