Come on... feet on the floor pan above the exhaust center box.
On my 97 disco a heatshield was never mounted on the exhaust and the same with any fixings.
As a heatshield is shown in the book, some models must have it, but, as you say could come loose and fall off.
Perhaps thats why LR fitted the heat resisting fibre mat to the underside as fitted to my disco.
Even if discodave got his gigsaw out and cut a heatshield how is it fitted, there no slots or screw holes on the exhaust centre box.