Such contracts should simply not be legal. Past owners should in generally speaking terms not be able to limit development and land use decisions of future owners. It’s no longer your land. You sold it. Want to privately limit rights via contract? Consider not selling.

If it gets zoned as parkland as part of a sale - great! You should be able to make that part of a sale contract. But if the governing body then votes to make it something else a decade later, that should simply be part of how things work.

Old people ossifying things to how they prefer via preventing future generations to freely operate is not how I want a society to run. If anything the older you get the less say in the future you should have.

> If they wanted a time limit, they could have put it in the contract, or not signed the contract.

Most contracts are legally mandated to have time limits. I think that's a good policy.

In this case an explicit number of years it has to stay a park would probably work better than an attempt at indefinitely defining the land.

There are some terms that are not allowed in a contract. I believe most deed restrictions are among those terms.