Put it in a unmarked box with a basic lock, assuming nobody has the trifecta of knowledge, skills and motive to uncover.
If anyone occasionally happens to see you writing in a journal and asks about it (though preferably it's best to save writing for private moments), you can just describe it as note-taking or brainstorming. If one considers these lies by omission, a more direct way would be a description of "personal notes." Then, the notes sound far less interesting for most people to look into.