Ask Lemmy

Certain types of burial allow the body to potentially contaminate nearby soil. Others can leave behind a void that can either collapse and disrupt nearby graves, or in some cases lift the body back to the surface in heavy rain. (Extremely uncommon now because essentially nowhere allows you to use those methods)

Funeral pyres or other forms of open air cremation are generally not legal due to concerns of fire spreading.
Whole body water burial is probably not legal in a body of fresh water in the US due mostly to the complexity of figuring out which law applies to that circumstance in any of the bodies of water that could be used that wouldn't be grossly undersized and unsanitary. (Basically that means the Great lakes, which are the only ones with the depth and size sufficient, but are shared between multiple states and also Canada. Usually the rule is that if it's not forbidden it's permitted, but body disposal is more complicated)

There's definitely some limitations. There was a bit of an issue in my state when a Mosque wanted to install a cemetery on their lot, but they were too close to the aquifer and weren't allowed.

I suspect it's different in different countries, but things like desecrating a corpse are often illegal. I expect if you carved it up and started throwing chunks around, that would be illegal even if it's what the deceased wanted. Probably storing the body away and not telling the authorities of the death would also be illegal

Word of warning though, check out the company before you do so. My mother in law was in the medical field and had a coworker that did this. The company ended up refusing the body because they had too many bodies. I've also heard of your body being used to test munitions, which is pretty much the opposite of what a lot of people would want.