Add shape only if shape doesn't already exist

[gtbreps_2]

I'm trying to add a text box shape. I have the code written to add the text box where I want it and how I want it formatted.

Dim Message As Integer
Dim messagebx As Shape
Message = MsgBox("Would you like to include a message to the client?", vbYesNo + vbQuestion, "Message")
If Message = vbYes Then
        Range("C12:L12").Merge
        rows("12:22").insert
            Set messagebx = Shapes.AddTextbox(msoTextOrientationHorizontal, 22, 165, 473, 185)
            messagebx.TextFrame.Characters.Text = "[Insert Message]"
            messagebx.TextFrame.Characters.Font.Size = 9
            messagebx.TextFrame.Characters.Font.Name = "Arial"
            messagebx.Line.Visible = msoFalse
        Else
        'do nothing
        End If

After this and a bunch of other code is performed, my sheet can be updated and the code re-ran. But if I re-run the code, this text box is replaced with a new blank box. I'd like it to just stay using an error handling statement or something. I'm just not familiar with error handling.