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)