Bus,
From the "indiscipline" you describe, you should make sure that all tasks are staged to wait for independant checks of the work before going on to other stages.
A sad indictment of the quality of your staff, I'm afraid.
Bee is quite right in stating what he has....but "complex" is whatever or whichever you (or your company) want to make it.
Complex depends on (naturally) the complexity of the work required, the quality of your staff, their qualifications, their competency and their capability.
If you feel 'they' need more stage checks and more supervision then it's your ball game - fill your boots and start the ball rolling.
hope this helps...