I've never seen/heard of a Stiletto main halyard locked at the masthead. Not sure how you do that. But, with the right halyard you shouldn't need to. Are you sure its the halyard moving or is the sail needing attention? Again, how is the halyard secured? Standard setup is a cleat just below the exit point on the mast but I have seen it go thru a rope clutch instead. Either works without any trouble.

Clayton