VeraCrypt (for example; previously TrueCrypt) allows for using separate passwords to access different data depending on which one was entered: one would be a dummy volume on which you would plant convincing data, and the other ("hidden") volume would contain your actual data. Since the encrypted data are indistinguishable (ideally!) from randomness, you have plausible deniability.
https://veracrypt.codeplex.com/wikipage?title=Plausible%20De...
Even if you cleared the device before it was taken into custody, they could still have a case if they can reasonably show that you cleared it with suspicion that it would be taken into custody. Obviously, that can be difficult to show, depending on the burden of proof required.
http://arstechnica.com/tech-policy/2015/09/forcing-suspects-...
(but they might just have you enter them yourself instead :/)