This example adds an oval to myDocument
and then places the oval second from the back in the z-order if there is at least one other shape on the document.
Set myDocument = Worksheets(1)
With myDocument.Shapes.AddShape(msoShapeOval, 100, 100, 100, 300)
While .ZOrderPosition > 2
.ZOrder msoSendBackward
Wend
End With