WPF border解决超出圆角边界的方法

<Border    BorderThickness="1"
                BorderBrush="Black"
                CornerRadius="8">
                <Border.Clip>
                    <RectangleGeometry
                        RadiusX="{Binding CornerRadius.TopLeft, RelativeSource={RelativeSource AncestorType={x:Type Border}}}"
                        RadiusY="{Binding RadiusX, RelativeSource={RelativeSource Self}}">
                        <RectangleGeometry.Rect>
                            <MultiBinding Converter="{StaticResource WidthAndHeightToRectConverter}">
                                <Binding Path="ActualWidth" RelativeSource="{RelativeSource AncestorType={x:Type Border}}" />
                                <Binding Path="ActualHeight" RelativeSource="{RelativeSource AncestorType={x:Type Border}}" />
                            </MultiBinding>
                        </RectangleGeometry.Rect>
                    </RectangleGeometry>
                </Border.Clip>  
<!--其他元素-->  
</Border>

    public class WidthAndHeightToRectConverter : IMultiValueConverter
    {
        public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)
        {
            double width = (double)values[0];
            double height = (double)values[1];
            return new Rect(0, 0, width, height);
        }
        public object[] ConvertBack(object value, Type[] targetTypes, object parameter, System.Globalization.CultureInfo culture)
        {
            throw new NotImplementedException();
        }
    }