Seems pretty straightforward: During the interview process give the applicant for the senior position a challenge such as you have faced in the past. Which parameters do they check first? What references do they consult? Once they reply, respond with a little more information--just as you learned from experience as it unfolded. How do they respond? Did they make the same mistakes you made when you were in the situation? Do they have novel insights or testing/programming methods? I use specific scenarios, based on personal experience, for each: network, database, programming, and people management skills--these seem to work well. Since these were real-world experiences, I gain insight into thought processes, as well as how candidates handle frustration with stymies--since each of the scenarios unfold in about 6-7 iterations, and become seemingly more and more intractable with each step. I prefer doing this as part of the oral interview rather than some grand technical closed door challenge.

Think back to your greatest challenges at work, I am sure you will remember a few doosies...if you haven't had any of your own DBA experiences and you are hiring a DBA, I really think you should consider outsourcing.