You could also have a daily cron job that runs “rndc freeze” and “rndc thaw”–that will cause the current version of the zone data to be dumped to the zone file, and the journal file to be deleted entirely. (This is problematic if you want to use IXFR, as the journal file is used to reconstruct older versions of the zone data.)
As for a daily cron job, the syntax is changing with 9.9 and this can be safely deferred until the next release.