Why "underneath ~ instead."? A simple "exile it." would be more correct (since "instead" is clearly wrong here, you cannot replace an event in the past, you will also want to replace the "would be" with is - unless you wanted a static ability, but why start that with "Whenever" which is a strong signal you don't create a static ability).

Also the location is entirely irrelevant to the rest of the card. The second triggered ability correctly refers to the cards exiled "by ~".

The activated ability is a bit lousy and does not further the theme. Stuck on with a glue-gun to justify the land part. But does that seem like an improvement?

Cut the activated ability and the land type for a simple mana cost.

Preventing cards from going to your own graveyard is rare. Even if it was on a land you wouldn't need that ability over a simple ": Add ."

I just heard about an above ground cemetery in Brazil and was attempting to depict that concept as a Magic card. Cemeteries feel like lands, I mean hey, Woodland Cemetery and all. It's true that I did really stretch on how to adapt a building to be a land bilby modern Magic standards. The exile underneath was solely for memory purposes so that players would not forget and accidentally include cards that had been exiled by other means.

There's no need for that, because it's common for players to put exiled things under what exiled them for as long as it matters. It doesn't mean anything, game-wise. It's just common practice.