Clearly the most absolute answer is to have every individual track and identify their own commits and changes to the computer system in an authoritative manner. Then you must balance each catastrophic failure against the reasonable expectation that the programmer could predict the outcome. Then you effectively strip the license to program (in that company/industry at least) from the offending 'rogue traders' when they try to run away with billions of dollars that was built on exploiting said catastrophe and get caught.