Best way of protect a backing field from mistaken use in C#

Question

I have a class (Foo) which lazy loads a property named (Bar). What is your preferred way to protect against mistaken use (due to intellisense or inexperienced staff) of the uninitialized backing field?

I can think of 3 options:

  class Foo {
    // option 1 - Easy to use this.bar by mistake. 
    string bar;
    string Bar {
        get {
            // logic to lazy load bar  
            return bar; 
        }
    }

    // option 2 - Harder to use this._bar by mistake. It is more obscure.
    string _bar2;
    string Bar2 {
        get {
            // logic to lazy load bar2  
            return _bar2;
        }
    }

    //option 3 - Very hard to use the backing field by mistake. 
    class BackingFields {
        public string bar; 
    }

    BackingFields fields = new BackingFields();

    string Bar3 {
        get {
            // logic to lazy load bar  
            return fields.bar;
        }
    }

}

Keep in mind, the only place I want people mucking around with the backing field bar is in setter and getter of the property. Everywhere else in the class they should always use this.Bar

Update

I am currently using the following Lazy implementation (not for all properties with backing fields, but for select ones that require lazy loading, synchronization and notification). It could be extended to support futures as well (force evaluation in a separate thread in a later time)

Note My implementation locks on read, cause it supports an external set.

Also, I would like to mention that I think this is a language limitation which can be overcome in Ruby for example.

You can implement lazy in this way.

x = lazy do
    puts "<<< Evaluating lazy value >>>"
    "lazy value"
end

puts x
# <<< Evaluating lazy value >>>
# lazy value

Answer 1

How about use of ObsoleteAttribute and #pragma - hard to miss it then!

    void Test1()
    {
        _prop = ""; // warning given
    }
    public string Prop
    {
#pragma warning disable 0618
        get { return _prop; }
        set { _prop = value; }
#pragma warning restore 0618
    }
    [Obsolete("This is the backing field for lazy data; do not use!!")]
    private string _prop;
    void Test2()
    {
        _prop = ""; // warning given
    }