How to Hide a Book Where No One Will Ever Find It

So, as I was watching Harry Potter and the Half-Blood Prince last night, this happened.

I don't know why the subtitles showed up like that on my computer, but you can fucking read. After Harry almost killed Malfoy, the only people that punished him were his friends, and they only made him hide the book where he got the spell he used. So he goes with Ginny to the Room of Requirement and she says, "we need to hide the Half-Blood Prince's book where no one will ever find it, including you."

Seems to me that the best place to hide a book you don't want anyone to ever find is a fire. Or a paper shredder. Or a paper shredder that's on fire. Pages can't be ripped or burned? Encase it in cement, use your stupid magic to make the cement look like an ordinary rock, and throw the damn thing into that gigantic lake you assholes have right next to the school. Look at all the shit in the room of requirement. It's pretty obvious that people are in this room quite a bit more than they are exploring the bottom of the lake with the monsters and freezing temperatures. This isn't one of those situations where hiding in plain sight is the best option.