Steel rebar will corrode if exposed to water correct? Does this mean exposed rebar cannot be buried due to the rain and ground water? I ask, because I want an exceedingly sturdy ground steak. What metals make good ground steaks or fence posts? What metals can handle being buried ?

Grounding stakes are for electrical grounding. Is this what you mean? Grounding "stakes" NEC states: "not less than 8ft' in length and, where steel, shall have the outer surface galvanized or otherwise metal coated for corrosion protection". Bare rebar must be encased in concrete. Almost all new home construction uses concrete encased rebar for grounding, placed in the house footing.
You mention "ground steaks(sic) or fence posts". Terms are not usually interchanged.

Forgive me, I did not mean grounding steaks at all then. I just mean something you can stick in dirt for years at a time that won't rust. And thank you, now I know rebar won't work. what will?

Copper... or copper plated ground rods are one option.

Stainless steel piping, PVC? Pressure treated posts.

It really depends on what forces will be applied and what is the use. A tent stake will not rust.