sounds good to me. then it'd be like the rather less portable Polisher which similarly has no grid ref (which may be pointless but it makes me feel a bit better). If anyone's desperate to see it they can always ask you for the details.
I've added a stone that's local to me without a grid reference. Mind you, it was ridiculously difficult to find until I created a new site group for it and its neighbours. Now at least you stand a vague chance of finding it.