I used to into CDG (a lot) and when a runway was out of use, the frogs would put up a giant flashing red 'X'.
It must have stood 20 feet tall and they stuck it on the threshold.
It was 100% effective.
Why not stick something similar near this taxiway before someone gets killed?
You can always switch it off or fold it down in the unlikely event of having to press this taxiway into service as a runway.