How do you get that second Prod Sec position?

I was working in TV for over two years as a Runner and got my first Prod Sec position last summer. I've since then been having trouble getting my second position as a Prod Sec. I had a couple of interviews last year for Prod Sec positions, but was unsuccessful. The feedback I got was that I lacked experience. I had to then go back to being a Runner. I was wondering if you had any advice on how I can go about getting that second Prod Sec position?