auto update dates

Sorry - I seem to be bombarding the list. I AM reading my copy of Bruce
Momjian's book quite closely, I promise!

I'm trying to make a rule to automatically update the time, date and
timestamp 'modified' fields when a row is updated.

This is what I have tried:

create rule ideas_insert_datetime_mod as on update to ideas
do
update ideas
set d_modified = CURRENT_DATE,
t_modified = CURRENT_TIME,
ts_modified = CURRENT_TIMESTAMP

This creates a cycle condition, and the rule does not operate.

Do I instead need to write a function and then trigger it after each
update action? I have 3 tables each with similar columns, with the same
column names, which I wish to update in the same way.

Thanks for any help.
Rory
--
Rory Campbell-Lange
<rory(at)campbell-lange(dot)net>
<www.campbell-lange.net>