Hi Rob,
You can also choose the query string parameters method, where you can describe what the query string parameter variable should be and populate the value on the link as a data field. Once the click occurs, you can then track every possible values that is captured.
Example: Let's say the query string is "campaignx" once this created you can then create the link as http://www.somewebsite.com?campaignx=<Span>Eloqua field name</span> You do want to apply some logic on the field value so can map it back to contact in a meaningful way.
Hope this helps.
Thanks
Amit