That's a really bad idea, especially if you're not a US citizen. If they want to access your computer, they _will_ call your superior back home and might tell him that they will either get the password or deny you entry.
In any case, if you are worried about protecting your data, you put yourself in a pretty bad situation if you rely on encrypting that data and hide the password. Bringing a relatively clean laptop will just avoid the issue altogether and will allow you to be cooperative with them.
Remember that they don't _need_ any cause to deny you entry or detain you, as long as you're not a US citizen.
Because messing with you is equally rewarding as "protecting the country."