lucy24 - 8:42 pm on Jan 6, 2013 (gmt 0)

park example.com as the secondary (or should I do a 301 redirect instead?)

Wipe that word "park" from your mind. If humans and/or search engines have been using both names, and you've already got past the "If it ain't broke don't fix it" point, then you've got no choice but to pick one name and redirect the other. The only remaining question is which.

The mechanics should be dead easy; you may not even need to create any new code. If the DNS points both names to the same place, your default canonicalization redirect -- the one that picks up with/without www. issues and similar -- will automatically deal with the "wrong" domain name as well.