Question on tombstones,grave yard and caskets in regards to law and property?

Captain_Fantasy had a interesting question that lead me to wonder what kind of legal/law problems would we run into if indeed we ran into having not enough space for human burial.

One solution was to simply re use the spots after they have decomposed , which is an excellent idea and logical.

But what about the grave yard itself? Who has say in that piece of land exactly?

and if I bought a tombstone and “that spot” then who are you to just take it off and re use it?

Not to mention the casket and body may not fully be decomposed (bones last a while correct?)is it fair for some one because lack of space to just go and dig up the site for space?