How to properly hide a base class property

Question

There is a base class (black box; can't modify it) that I derive from. In my derived class, I no longer want to allow users to use a property, instead I have a public function now to use instead. I won't go into the details of why (it is irrelevant), but here is the property I'm trying to hide:

public ComboBoxItemCollection Items { get; }

I've tried this, but it didn't work:

private new ComboBoxItemCollection Items { get; set; }

I also tried this, however the compiler says I am not allowed to make both accessors private:

public new ComboBoxItemCollection Items { private get; private set; }

How do I properly accomplish this? Note that I'm not depending on this being a complete security solution, obviously through means of casting to the base class they can still call this property. This is simply meant to offer the user a compile-time error, which helps guide them to realize they cannot use this property and instead should use the new function in the derived class.

EDIT

Thanks to the answers in this thread, I came up with the following solution:

    [Obsolete( "This property is obsolete. Please use MRUIdComboBox.AddItem() instead.", true )]
    public new ComboBoxItemCollection Items
    {
        get
        {
            throw new NotSupportedException( "This property is not supported. Please use MRUIdComboBox.AddItem() instead." );
        }
    }

Answer 1

You can't. The closest you could come would be:

[Obsolete(IsError=true)]
public new ComboBoxItemCollection Items
{
    get { return base.Items; } // Or throw an exception
}

Personally I'd be tempted to ask whether you should really be deriving from this if you don't want all the members though... can you use composition instead?