I saw a video on this, honestly just seems like it'd work. And if it doesn't, well, the bottom of the literal sea seems like a good place to put stuff to avoid people stumbling upon it.
ie we know nothing much about that area... who's to say it wont suddenly turn up on a beach or in fish or plant life after 50 years of being down there...?
erm, the literal 10 kilometers of water above them?
Also Mariana Trench is called a trench because is a trench. A trench 10 km deep.
We dont know what we dont know... what else do we not know?