they have to find the encrypted files first. Disguise them and only boot into them using something like hiren's bootcd that boots up in RAM only. Plausible denyability is the best course of action. If you don't want evidence of your activities to be present don't do anything using your primary windows operating system where stuff gets stored in the registry, and anything data that is saved to a hard drive can potentially be recovered or used as evidence against you, or you could potentially get infected with keyloggers or trojans (many people back up their bitcoins in clean environments like these) . Boot and use RAM ONLY, and do a clean shutdown when finished and pull the power cord so the RAM loses it's stored energy and wipes clean.
Myself I've got nothing to hide that the government would care about so I just secure passwords with encrypted 7z files that use random 32 character passwords I store as QR codes and keep in my wallet. I use a 2D barcode scanner when I want to access the information. Plus I know my system is clean from anything a random hacker might use so no problems there. Although I am against NSA spying into everyone's lives simply because I don't believe in the drug wars that governments worldwide insist on engaging in, I myself have not too much to hide so meh... as a Caucasian male I'm less likely to get hassle to begin with, although as a Caucasian male it also means i have to work for my money, I don't just get it handed to me like members of the opposite sex or other races might, but that's a topic for another discussion.