To disable click tracking for individual links in a Freeform HTML or Canvas email you must insert 'nr_' before the 'http:' of a given link.
For example: <a href="nr_http://www.verticalresponse.com" >VerticalResponse</a>.
You can also disable tracking in a Text Only email by inserting nr_ before the http of a given link within the email text itself.
For example: nr_http://www.verticalresponse.com
When you do this the link will not be encoded with the VerticalResponse tracking redirect. Clicks on these links will not be tracked in the VerticalResponse reporting for this email campaign.