see 

WPF_Control_OutlineLabel.cs

public class OutlineLabel : Control,INotifyPropertyChanged
    {
        public static readonly DependencyProperty OutlineForeColorProperty =
            DependencyProperty.Register ("OutlineForeColor", typeof (Color), typeof (OutlineLabel), new PropertyMetadata (Colors.Green));

        public static readonly DependencyProperty OutlineWidthProperty =
            DependencyProperty.Register ("OutlineWidth", typeof (double), typeof (OutlineLabel), new PropertyMetadata (2.0));
        
        public static readonly DependencyProperty TextProperty =
            DependencyProperty.Register ("Text", typeof (string), typeof (OutlineLabel), 
                new FrameworkPropertyMetadata (null,
                    FrameworkPropertyMetadataOptions.AffectsRender | 
                    FrameworkPropertyMetadataOptions.BindsTwoWayByDefault,
                    CustomTextBox_OnTextPropertyChanged));
        

        private static void CustomTextBox_OnTextPropertyChanged(DependencyObject d,
                     DependencyPropertyChangedEventArgs e)
        {
            OutlineLabel outlineLabel = d as OutlineLabel;

            outlineLabel.SetValue (TextProperty, e.NewValue);   
            outlineLabel.Text = e.NewValue.ToString ();
            outlineLabel.UpdateLayout();
        }

        //public OutlineLabel()
        //{
        //    //    DefaultStyleKey = typeof (OutlineLabel);
        //    DefaultStyleKeyProperty.OverrideMetadata(typeof (OutlineLabel),
        //        new FrameworkPropertyMetadata (typeof (OutlineLabel)));
        //}

        public Color OutlineForeColor
        {
            get { return (Color)GetValue (OutlineForeColorProperty); }
            set { SetValue (OutlineForeColorProperty, value); }
        }

        public double OutlineWidth
        {
            get { return (double)GetValue (OutlineWidthProperty); }
            set { SetValue (OutlineWidthProperty, value); }
        }

        public string Text
        {
            get { r