To be explicit, if one separates ownership rights and development rights, and gives the development easement to a conservation trust/foundation that has a mandate to never sell them, I guess things will go better. There are land conservation trusts all over the US and if there isn't one you can create one.

To be clear, I guess that a city who had ownership rights but not development rights could be stupid and ignore a conservation easement, but I guess that is not likely.