So, this has happened twice and I wanted to share.

If it rains a lot and I drive my '03 Disco II through a few puddles, my SES light comes on. I just wanted to share my experience that, once I drive around a few times (to dry everything out and after a few engine cycles have taken place correctly) it is possible to shut the light off by doing the whole "push the trip odometer rod-button in, turn key to "2" (accessories on), wait five seconds, release rod, turn key off, start car" thing. I don't know if this is common knowledge but wanted to share it with the forum. It does not seem to be an automatic way to reset the code as it won't happen until you've driven around a while to dry everything out, but it works after 12 hours or so.