I suppose a hidden volume would be the way to go in this instance (assuming you were one wanting to hide something) as a court would order you to decrypt the drive, you would provide a key for the decoy drive and proving that you have provided a decoy key would be incredibly difficult.
Is a hidden volume enough to acquit you? What if the judge is smart enough to know this feature and requires you to hand over the second key? There's no way to prove if there is indeed a hidden volume, can you still be held in contempt for not providing the key to a 'only you knows' existing or non-existing hidden volume?
Thats not how it works
Have a look here: