Hi, Ramilahs, I've finally spotted your query.
Loose stones are scree and, if we're to add to that in a way that gels with 'guarded', presumably the whole word is 'screened'. The only justification for 'ned' that I can see is if you remove some of the centre - a diameter being a central measure - of 'needed', you're left with 'ned'. I'm far from convinced by that, incidentally!
I even toyed with 'tautness', as when something is loose, that's what's needed.
In the end, I went for 'tactless', as you did, though that's far from the first opposite of 'screened' I'd have thought of myself. Time will tell.