and corrode it, rather than the steel tank because those metals give themselves up more freely than iron. Clean the rod about every three years with a rotary wire brush, and when it becomes too decomposed to consider keeping, replace the rod. (MUCH cheaper than a water heater!)
3) Drain a few gallons from the tank through its water bib every few months to remove sediment that collects in the bottom of the tank, and your tank (especially a gas fired one) will last longer because water will not be heated through an insulating layer of crud, requiring more heat, higher fuel costs, and shorter tank life.
Follow the preceding steps and your heater will last much longer! Ignore them, and pay the price for your laziness/forgetfulness. Putting a white sticker on the tank for recording your maintenance steps, and you'll remember what you've done, and what you'll need to do.