Over the top of the parse of the data being valid (the content confirms to the standard) there is nothing. TCP offers some protection.
Depending on where you're trying to protect you could consider adding a hash to the response so you can verify that the received content matches the sent content.
From an SDK standpoint you have KVC validation (which RestKit ties into heavily). This allows you to check each field of each object during the mapping process and bin any objects that fail the validation checks.