you may add a column (such as part_mnth number(2)) which is partitioned. you can write a trigger to insert/update this column whenever records are added/updated.

note: Keeping as number field has some advantage, becaz you can easily add, substrat, mod (useful when u automate the truncation of old partitions)

Also, u may need some sort of job queue/scheduled job to purge/truncate the old partitions whenever the date rolls back to the next year.