Re: What GPS really needs
What those lorry drivers are doing is negligence and unlawful property damage, so they have no excuses.
My suggestion would be to embed well supported replaceable heavy duty cutting tools * level with the stones, at a position designed to cause the maximum damage to their wheels/tires if they damage the wall, and add a fair warning road width hazard notice on your land!
* The kind of tools use by industrial steel cutting lathes.
As for the article, I think there will need to be ground based edge/location beacons before I'd fully trust GPS like navigation, and easy to detect hard boundary & boundary/entrance indicator materials to aid much better edge detection for well over fastest speed stopping distance before I'd trust self-drive cars. Any boundary materials would need to be detectable in fog or otherwise visually obscured, possibly using low power radar.