AVR-Chat

>
>Another thought is to use Hamming codes and write multiple copies. The
>AVR has way more EEPROM than I really need as I have only about 20 bytes
>total of parameters, plus need for a summing register.

An approach I've used, is to start with it erased, and do readback 
verify on the data.
When area X fails, then you move to area Y.
To read the data, or to start again after a power failure, you scan 
till you find FFFF...FF (erased data) then you back up a notch, and 
that's the active area.

So, if you had 8 bytes to write, you'd maybe start at location $0008 
(avoiding zero)
Then when $0008-$000F wear out, you move to $0010-$0007 and so on.
It's simple and straightforward.