I don’t suspect page1067’s possibilities would be enforceable. As long as op has a lawful right to post what he has and it is not libelous, concerns such as extortion or tortious interference wouldn’t apply anymore than it would to a spiteful neighbor painting their home lime green to piss off everybody.
Depending on the actual topographical specs, builder may have an issue with either creating a hazardous condition where a person injured due to the “cliff” could successfully sue the builder or if it creates a concern for op such as causing a concern of a landslide damaging ops property.
so, it’s time for an engineer and a lawyer to review the situation. If the cliff does not endanger ops property, he has no lawful right to demand builder do anything. If it does create a concern of erosion or a landslide, op has a basis to demand builder shore up the land to prevent erosion or a landslide. If it is a hazard for injury, in a legal concern, then op would likely be relegated to seeking the local municipality take action to force builder to make the area safe.
If neither apply, well, op can build his own fence to block the view and protect his grandchildren. If builder is under no legal obligation or concern for liability, op may be fighting a losing battle.