Recording historical session stats and events

I would like to make Oracle record session stats and events whenever a session ends. Is there any reason I can't put a trigger on SYS.AUD$ that collects stats and events whenever a disconnect occurs?

Potential problems:

1.) Is the session already gone when the audit stuff is firing off?

2.) Should I be really, really careful about putting a trigger on a data dictionary table? Why?

Anyway, I think I'll try it on a test instance. This would be really cool if it worked.

--
Jeremiah Wilton      http://www.wolfenet.com/~jeremiah