Disk Protect v2.1 for GEOS by Rober L. Thaller (Released 9/16/1988) is a utility that will let you change a disk into a Master or Boot disk, making it impossible to delete files from the DeskTop.  It also works the other way around.

This program was found on issue 10 of "Disk O' Quarter" put out by the Commodore Users of Wichita.