Based on my understanding, tokens cannot be trackable. If the token contains a URL (a field type of "string"; and does not contain the http:// protocol), you need to add "http://" just before the token. For example: "http://{{lead.customURL}}". This would now be trackable. This probably doesn't apply here, but just thought I'd provide some additional insight when using tokens. We have a custom field (type "URL") where the full URL (including the http://) is part of the value. Unfortunately Marketo is unable to add tracking code here since the full URL is contained in a token.