If you have a pressure cooker, it's a piece of cake. Everything I learned, I learned from this:
https://www.pressurecookrecipes.com/instant-pot-bone-broth/
This would only work if the rooster is show quality.
Two feet down, at least, so that raccoons or other animals won't be able to smell it and dig it up.
I did this in my garden. The plants that grew in that spot grew VERY well. A carcass has a LOT of nutrients to add back into the soil.