I can imagine other, possibly smarter and wittier, works.
I could, for instance, fashion replica national park wildlife information signs that contain information about the nature of illegal dumping activities. These could be placed prominently next to various dumping sites. They may drolly refer to the nocturnal activities of the genus scumbagus wollongongus, etc. Additionally there could be wildlife tours of the relevant sites, with little brochures and maps depicting particular routes, features and views. But all of this, however potentially useful as an intervention, strays away from my genuine, unfunny, confused response to the wrecked vehicles and associated rubbish. That is why I prefer a less sophisticated response.
Remaining with my current strategy of cutting, it is clearly possible to imagine carving something more elaborate and precise, even whimsical, but this risks detracting from the naivete of the square shape. Crucially, for me, the roughness of the latter indicates a kind of failure of response. If it is eloquent at all, it is precisely in terms of its directness, simplicity and manifest inadequacy. It is as abject as the cars themselves.