[stcredzero]

If you are really worried about this, I recommend surgery.

There might be a Kickstarter product in this. Simply devise a magnetic activation switch for the microphone. I've opened up multiple 13" Macbook Pro laptops, so I know how little space is in that corner where the microphone and magsafe socket board is, but there is enough.

Perhaps even better: a microphone that has a deactivation pin which can be pulled with a pair of tweezers. A service would solder this in place for you, and the laptop could be used with no internal microphone. Then, when it was time for you to sell the laptop, you simply open the case and pull the pin out of the back of the microphone, reactivating it. You could even construct this out of the same microphone element as used in the macbook. Just have the pin short across the mic capsule's terminals.