want sudo but not sudo su - how

[John]

Greetings, freebsd-questions

I want to put operators in sudo BUT I don't want them to sudo su -
because after they do that, subsequent commands enacted as root don't
appear in the logs. The desired behaviour would be sudo su command (any
command) but not sudo su -, for these users. Is there a way of enforcing
this?

The reason being that if they do something and the server eg goes
titsup, I want to see what was done in the logs. Would be grateful for
any assistance the list may have.
-- 
John