Catching DDL events (or equivalent functionality)

Hi,

I know that you can not (and maybe should not) install triggers
on system catalogs. But, if I want to catch certain DDL events
(such as adding a column), is there any way to do it in PostgreSQL?

Maybe, it could be useful that the triggers (installed on normal tables)
can be fired not only by DML but by DDL events.

Thanks in advance.

Regards,
The F. Jackal.