setting locks on dconf keys

Hi all,

from: http://live.gnome.org/dconf/SystemAdminstrators it should be 
possible to set locks on specific keys:

'Settings from 'local' would take priority over settings from 'site', 
but locks installed in 'site' would take priority over 'local' (and 
'user').'

But I cannot find any information how to lock a key.

Kind Regards
Marcus