query help

I have a table called "marketing_campaigns":

marketing_campaigns:
+----+--------------+------------+-------------+-------------
| id | date_started | date_ended | property_id | status
+----+--------------+------------+-------------+-------------
| 1 | 2005-01-01 | 2005-03-12 | 5 | sold
| 2 | 2006-01-11 | 2006-02-23 | 5 | jointly sold
| 3 | 2006-05-13 | NULL | 5 | for sale
| 4 | 2006-02-01 | 2006-02-06 | 6 | sold

I am having trouble trying to say: Only show old campaigns And only if
their is not a "current" campaign for this property(property_id)

The result of the query should only return row 4. Is their a way to do this
in sql without resorting to proprietary functions, or should I resort to
using Ruby (rails app)