Ummm...no land, no property line, thus no property. And with that, no ownership of property exists because there is no more property.
Many have asked what if their home falls down to the cul-de-sac below, and the quick answer is you're SOL.
What can one do? Don't build near the beach! If you want a home with a view, at least in L.A., build in the Hollywood Hills where it's a rock, not sand foundation.
As is, people in Laguna Beach are up in arms, blaming all this on development and the continual shifting of the hillside each time a shovel's load of soil is removed to plant these 5 to 10,000 square-foot homes, and the fact is, they're right. Maybe they'll sue the contractors or the city or state. But who knows. They're still sleeping in a rented motel room.