It is OK I have solved the problem

A)

 <Intersoft:UXDesktop x:Name="uxDesktop" Background="{x:Null}" TaskBar="{Binding Path=DeskTopDock, ElementName=MyNavigation, Mode=OneWay}"

<my:Navigation x:Name="MyNavigation" Visibility="Visible"/>

B) In the code behind for the Navigation User Control

 public partial class Navigation : UserControl
    {
        #region Constructors and Destructors

        /// <summary>
        /// Initializes a new instance of the <see cref="Navigation"/> class.
        /// </summary>
        public Navigation()
        {
            this.InitializeComponent();
            this.DeskTopDock = this.desktopDock;
        }

        #endregion

        #region Properties

        /// <summary>
        /// Gets DeskTopDock.
        /// </summary>
        public UXDesktopDock DeskTopDock { get; private set; }

        #endregion
    }