I'm giving my external HDD to a friend tomorrow for a few days. It's partitioned via Master Boot Record and there are two partitions: a NTFS partition and my Time Machine partition. I don't want him to be able to access the latter, but I can't turn the encryption on because the disk would have to be partitioned with GUID.
Changing the partition scheme would require me to reformat the disk. I can't do this either, as I don't have another HDD to put my files on in the meantime.
Is there another way to encrypt the partition, other than the built-in option of OS X? Or is there a way to prohibit access to the Time Machine partition without any encryption at all?