As of Nethack 3.6.0 Elbereth no longer works on a square that you're not standing on, so it can't be used to guard a stash. Now you need to use a scroll of scar

As of Nethack 3.6.0 Elbereth no longer works on a square that you're not standing on, so it can't be used to guard a stash. Now you need to use a scroll of scare monster for that purpose.