Instead of letting everything get serialized by default, you can take the "opt-in" approach. In this scenario, only the properties you specify are allowed to be serialized. You do this with the DataContractAttribute and DataMemberAttribute, found in the System.Runtime.Serialization namespace.
The DataContactAttribute is applied to the class, and the DataMemberAttribute is applied to each member you want to be serialized:
[DataContract]
public class MyClass {
[DataMember]
public int Id { get; set;} // Serialized
[DataMember]
public string Name { get; set; } // Serialized
public string DontExposeMe { get; set; } // Will not be serialized
}
Dare I say this is a better approach because it forces you to make explicit decisions about what will or will not make it through serialization. It also allows your model classes to live in a project by themselves, without taking a dependency on JSON.net just because somewhere else you happen to be serializing them with JSON.net.