Actually, you're not entirely correct. In a PUBLIC building (including offices) there is no assumption of privacy - so while the boss may not be able to have a tape recorder running in the desk drawer, if the security system they have in place records both audio and video they CAN use that for evidence.
The part I don't get is that you seem unwilling to use any of the solutions we've suggested - the easiest and best of which is a portable white board or PDA.
You say you don't want to be bothered to carry anything around that would allow you to communicate in a manner that allows you to "wipe" your conversation (portable/fold-able white board, PDA etc) and would put YOU in control - but then you whine and complain about the fact that THEY are keeping THEIR paper after you use it (which is ironic considering you are demanding they use THEIR paper, which DOES give them the right to KEEP IT, because it's THEIR PROPERTY!!)
I don't mean to be rude - but judging by your posts, I'm going to guess that you write some less than "smart" things on your notes. I mean on this thread you've been a racist, a smartass, and just obnoxious ... and honestly if you write like that to your boss (or talk like that via the interpreter) I'm more than a little shocked that you are still working there because here racial slurs and derogatory remarks are plenty to get you instantly fired.
The ADA and other laws are NOT in place to remove accountability (you write well enough that if you say something offensive/racist etc in a note you know what you've said, it's not a language problem) it's meant to provide critical access and prevent employers from refusing to hire someone who CAN do the job simply because that person is disabled.
If you write a stupid note to your boss ... or admit to your boss in writing that you hit/yelled at them/use a slur towards/stole from someone etc THAT is on YOU ... it's a totally separate issue from ADA. If you have requested an interpreter for a disciplinary or other official meeting and then decide to write a note regarding that situation without the interpreter present - that's YOUR fault, not your boss - all you have to write is "I require an interpreter present before discussing this. thank you" and THAT'S IT!