Lol that is a diary though, by its intent and purpose. If you're worried someone might find them, hide them at the bottom of shoeboxes with other papers and books on top. If you've got bookshelves angle a shelf away from the wall and hide them behind there. I used to keep 1 hidden at the bottom of my laundry basket wrapped in a black plastic. You can also keep them hidden at the bottom of your cupboard under a stash of clothes that doesn't get rotated often. Tape 1 to the top of the inside of a drawer. or under your desk. Hide one under the mattress.
hmm I guess it depends on your definition of a diary. I see it as something you have to write in everyday about what happened that day, which isn't what I do. it doesn't really matter hahaha, i was just trying to stress a point!