Wii sucks...

If he's not smart enough, the just do the following: RAR the folder with your stuff inside (including all the exported passwords, bookmarks and all). Password protect the RAR file. Put it in another folder. Rename the folder to something daunting like sysfiles.bk (rename the rar to something like this too) or something and if you can, password protect it (many s.w available on the net). Finally, if you can (and want to) put the files in WINDOWS folder and hide it.

Viola...

or set up a ghost drive.