I have a property in FL where the buyer has defaulted under the terms of the contract for deed. I have sent three notices, all unanswered... what do I need to record to end this contract? It is just for bare land so there is no need to evict, etc.

What are the terms of the contract, in all of mine, it clearly states that upon default and notification, the contract converts to a month to month rental.

Remember these contracts are not filed as deeds, but are merely a contract.
So proper legal notice as to the default and your action to end the contract is all that should be needed.

I would have them served legal notice as proof.