how to stop overlapping controls runtime.

Thumb addthumb = new Thumb();

                    addthumb.Height = 20;

                    addthumb.Width = lenght_[i]+25;

                    addthumb.Name = "L" + i.ToString() + "P" + i.ToString();

                    addthumb.Background = System.Windows.Media.Brushes.Orange;

                    addthumb.DragDelta += new DragDeltaEventHandler(myThumb_DragDelta);

                    Canvas.SetLeft(addthumb, position_array[balls]+25);

                    Canvas.SetTop(addthumb, 20);

                    canvas_container.Children.Add(addthumb);

 

private void myThumb_DragDelta(object sender, System.Windows.Controls.Primitives.DragDeltaEventArgs e)

       {

           FrameworkElement element = sender as FrameworkElement;

           Canvas.SetLeft(element, Canvas.GetLeft(element) + e.HorizontalChange);

           lbl_Heightshow.Content = element.Height;

           lbl_widthshow.Content = element.Width;

           lbl_Slub_name.Content = element.Name;

           lbl_leftposition.Content = Canvas.GetLeft(element).ToString();

           if (Canvas.GetLeft(element) == 0)

           {

               lbl_leftposition.Content = "0";

           }

           else if (Canvas.GetLeft(element) < 0)

           {

               lbl_leftposition.Content = "0";

               Canvas.SetLeft(element, 0);

           }

           else if (Canvas.GetLeft(element) + element.Width > canvas_container.ActualWidth)

           {

               lbl_leftposition.Content = (canvas_container.ActualWidth - element.Width).ToString();

               Canvas.SetLeft(element, canvas_container.ActualWidth - element.Width);

           }

}

now what i want is...
 
the generated 'thums' should not overlap each on other while we drag them on the canvas.
 
please help and Thanks.