All shipping containers are traceable, worldwide by linked official computer systems. It is very simple to identify containers carrying any live breathing animal, including a human cargo. To run a successful smuggling business you would need insiders who can secretly mark your containers on the system to avoid pseudo-random customs inspections. You could even mark your competitors' containers to be inspected! (Such a system would need backup by the usual gangster methods to deal with honest inspectors who somehow stay in the job). Find the programmer, offer him and his family protection and you can break the code. It has to be a military solution, of course, when the whole system is compromised.