C#

protected override void OnLocationChanged(EventArgs e)
{
    if(DesignMode)
    {
        //Do what you whant here
    }

    base.OnLocationChanged (e);
}

<pre>using System;
using System.Collections.Generic;
using System.Text;
using System.Windows.Forms.Design;
using System.Drawing;
using System.Windows.Forms;
using System.Drawing.Drawing2D;
using System.ComponentModel;

namespace WindowsApplication1
{
    [Designer(typeof(SomeControlDesigner))]
    public class SomeControl : Control
    {
        public SomeControl()
        {
            this.Size = new Size(100, 25);
        }

        protected override void OnPaint(PaintEventArgs e)
        {
            base.OnPaint(e);

            using (LinearGradientBrush brsh = new LinearGradientBrush(this.ClientRectangle,
                   Color.CornflowerBlue, Color.White, LinearGradientMode.Vertical))
            {
                e.Graphics.FillRectangle(brsh, e.ClipRectangle);
            }
        }
    }

    public class SomeControlDesigner : ControlDesigner
    {
        // This is the key step.  Using this override, you can pretty much completely
        // customize the way the control appears on the designer.  I've used this in my controls
        // to completely change the design-time appearance of controls to make their design 
        // capabilities more obvious.
        protected override void OnPaintAdornments(System.Windows.Forms.PaintEventArgs pe)
        {
            base.OnPaintAdornments(pe);
            using(SolidBrush brsh = new SolidBrush(Color.Red))
            {
                pe.Graphics.DrawString(this.Control.Location.ToString(), this.Control.Font, 
                                       brsh, pe.ClipRectangle.Location);
            }
        }
    }
}</pre> <br />
<br />
The OnPaint override is there just to make the point that this is a custom control.  You'll also need to add a reference to System.Design.dll.