Named stops randomly - domains down

On one of our servers Named just stops causing no domains to work.
It can go 4-5 days and then it stops again and so on....
I just run: service named starts and named starts again but why does it stop in the first plave. It's really a pain in the ass.

Anyone know why this can happen ?
Can I add "service named start" as command in cron or does it need to be a script ?