Land rovers are not water-proof. The only engine you may rely on deep fording is the naturally aspirated diesel engine of Land Rover with a raised in take. No electronics involved and you may go as deep as you have a grip.
As for the rest of the Landie (the passenger cabin etc.) they are not even rain tight <img src="/images/graemlins/smile.gif" alt="" />
Stock Military Unimogs can ford up to 4 feet of water easily.