Use antifreeze recommended for alloy engines in the recommended mix ratio. It prevents corrosion and raises the boiling temp: both very useful things. Antifreeze's corrosion resistance declines with time so replace as recommended by the manufacturer.
I'm with John on this one, definitely keep it simple and known technology. The zinc anode idea has great appeal at first sight but it's not so simple as just bolting a lump of zinc onto the target area.
/boring geek mode/
Galvanic protection (other terms available) is very much dependant on the position of the anode/cathode in the galvanic series (
https://en.wikipedia.org/wiki/Galvanic_series ), the electrolyte and relative surface areas. It's got nothing to do with how hard or soft the metal is as inferred to in the hotrod article and although it might sound conceited, I'm skeptical of some of the logic/terminology used there.
I'm not sure on modern terminology but we used to refer to "throwing power" as the area protected by an anode. Basically, if you bolt a lump of zinc onto a mild steel plate in a conducting liquid then the area immediately adjacent to the zinc is very well protected because the current flow between the zinc/steel is high. The further you go away from the zinc the wider the area to protect and lower the beneficial current. At some point you end up with not enough current to protect the steel and it rusts. Galvanic protection often requires more than one anode to give complete protection but in properly designed applications or galvanised steel, it is very good.
It's one of those things which look very simple but often requires more consideration than you might first think. When I was working we used systems like this on some pipelines because it's easily monitored, but it wasn't a universal application. The most common I knew of was on boats and that's well sorted, I wouldn't be surprised if you couldn't just dial in the hull size and read off the number, size and placement of anodes from a list in a shop.
But as for a system to protect a cylinder head, I'm not sure where I'd start. It's certainly do-able but I'd have no idea of the size or location of zinc anodes and I'd guess we'd need more than one to balance the system.
So I'm with John and keep with antifreeze which is basically corrosion protection via water treatment. It's 100% effective when done properly and reaches every nook & cranny in your engine - wherever the water goes, protection follows. Service life depends on the concentration or type of chemicals used for protection because, as you might expect, they get depleted due to chemical reaction over time. Your antifreeze might still not freeze at -20C but it could have run out of corrosion protection, so I tend to follow the recommendations on the tin for changing.
