The Show Desktop tool, usually part of the Quick launch bar, is not an ordinary program shortcut. If it is deleted, the procedure for re-creating it is not obvious. Follow these steps:

Open Notepad and type the following text:

[Shell]
Command=2
IconFile=explorer.exe,3
[Taskbar] Command=ToggleDesktop

Save the new file as Show Desktop.scf.

Drag the file’s icon to the Quick Launch bar or any other location where you want the shortcut to appear.