See Secure Deletion of Data from Magnetic and Solid-State Memory: "Since degaussing destroys the sync bytes, ID fields, error correction information, and other paraphernalia needed to identify sectors on the media, thus rendering the drive unusable, it makes the degaussing process mostly equivalent to physical destruction."

This paper is cited in the documentation of the shred program, which uses 25 passes of overwriting as the default. shred -u -z -f $* seems to work okay in place of /bin/rm.