- Keep it in a sealed container, otherwise it'll dry out completely in a couple weeks and become inedible
- Put a single folded-up paper towel in the sealed container to absorb gradual amounts of moisture that come out. Otherwise condensation will form on the cheese and mold will grow quickly
- Replace the paper towel with a new one every 2 weeks (it'll be slightly damp)
- Keep the hunk solid (don't pre-cut) and always grate/shave from the "oldest" area. Mold only grows on the surface, so as long as you're using it once every week or two, the surface doesn't exist for too long, so zero mold
- Cut off the rind before any of this, since otherwise it would accumulate mold eventually. Save rinds in the freezer until you make minestrone or another appropriate soup, and cook with them -- they'll stay solid but the soup will absorb all the flavor from the rind, and then you fish it back out at the end
Maybe it sounds like a lot of work, but a $50 chunk can last half the year if you're using it by yourself every couple days for scrambled eggs, simple pastas, shavings on salads, and so on. It turns out to be a pretty affordable luxury.
Before I had that, I would usually wrap the cheese in a layer of wax paper, followed by a layer of foil, and put that in the freezer, taking it out as I needed it. Hard cheeses in the freezer will turn white and may no longer be useful to eat shards of on their own, but they're still fine for grating and melting.
Do you keep it in the fridge, wrapped, what?
How do you store it so it lasts so long?