The GUID Partition Table (GPT) is unique in that it resides both at the beginning and the end of a disk. Its removal is not as simple as zeroing out the first 512 (or 446) bytes.

For demonstration, I have a Seagate 750GB drive with a device name `sdb`

Figure out where to start zeroing

    [root@livecd centos]# fdisk -s /dev/sdb
    732574584

This is the total number of blocks; we'll zero out the last 100,000 blocks:

    dd if=/dev/zero of=/dev/sdb seek=732500000 bs=1k

Now zero out the first 1000 (overkill, really)

    dd if=/dev/zero of=/dev/sdb count=1000 bs=1k

Ta da!

## Sources

*   [GPT Removal](http://www.digital52.com/help/gptremoval.html)