How to remove the close button in DockingManager?

//Option 1
private void SetCaptionBtnOptions()
{
//Hide the CloseButton for all the Controls that are DockEnabled.
for (int i = 0; i < this._dockingMgr.CaptionButtons.Count; i++)
{
if (this._dockingMgr.CaptionButtons[i].Name == "CloseButton")
{
this._dockingMgr.CaptionButtons.RemoveAt(i);
}
}
}
//Option 2
//Hide the CloseButton for all the Controls that are DockEnabled
this.dockingManager1.CloseEnabled = false;

'Option 1
Private Sub SetCaptionBtnOptions()
'Hide the CloseButton for all the Controls that are DockEnabled.
Dim i As Integer = 0
Do While i < Me.dockingManager1.CaptionButtons.Count
If Me.dockingManager1.CaptionButtons(i).Name = "CloseButton" Then
Me.dockingManager1.CaptionButtons.RemoveAt(i)
End If
i += 1
Loop
End Sub
'Option 2
'Hide the CloseButton for all the Controls that are DockEnabled.
this.dockingManager1.CloseEnabled = false;