how to password protect ext drive

I am using 2 WD Passport ext drives for backups. I am using Time Machine and I also have several directories that I also copy there. Is there a way to put password protection on the ext drives?

You can protect an external drive with a password in Disk Utility as part of the Erase/Reformat process.
However, I believe it cannot be done without losing existing data, so you would need to back it up first, then write it out again afterwards.
Jonathan

Don't do that unti you know for sure how Time Machine handles encrypted backups. I know there is such a thing but I'm not sure whether you need to setup encryption before the first backup or whether you can do it to an existing backup.

I have used encrypted TM disks, and have not encountered any issues, apart from that mentioned above, of erasing the disk initially. I have also subsequently copied the TM backups to the encrypted disk, and tested restore of individual files.

thanks for the replies. I guess losing existing files will not be a big deal, other than the time to re-backup, seeing as how they are just backups, and 2 redundant backups at that. I also wanted to be sure that I would not have a problem using them for a complete system restore should it ever come to that. I am a more recent (16 mos.) convert from windows to mac so I have not yet any experience with restoring a mac.