Best practice question

Hi
I am going to add a new column to a table for modify_date that needs to be
updated every time the table is updated. Is it better to just update
application code to set the modify_date to current_time, or create a
Before-Update trigger on the table that will update the modify_date column
to current_timestamp when the table is updated? I also have slony in place,
so the trigger will need to be on master and slave. Slony will take care of
suppressing it on the slave and enabling in the event of a switchover, but
it is additional overhead and validation to make sure nothing failed on
switchover.

So considering that we have slony, is it better to use application code to
update the modify_date or use a trigger? Is a trigger essentially 2 updates
to the table? Are there any other risks in using the trigger?

Thanks

Tory Blue