Identifying Duplicate Text Strings In A Column

with creating this macro to identify duplicate text strings in a column, which is great.

But, I'd like to be able to identify them by changing the text of the subsequent duplicates that are found.

For example, if 3 cells in a column are 1111, I'd like to add a string of text to the end of the 2nd & 3rd cell, but not the 1st cell.
1111
dup-1111
dup-1111-dup

This will enable me to sort the column and find the duplicate easier than just visually.

Sub color_dup()
Dim r As Range, rng As Range, Col As String
Col = "d"
Set rng = Range(Col & ":" & Col)
rng.Interior.ColorIndex = 0
For Each r In Range(Col & "1", Range(Col & "65536").End(xlUp))
If Application.CountIf(rng, r) > 1 Then
r.Interior.ColorIndex = 6
End If
Next
End Sub