When making a stump garden, how far do you bury the stumps? How do I keep the stumps from rotting?

Never heard of a stump garden. That's a new one for me after nearly 20 years of gardening. However, the wood from the stumps will eventually rot, no way to stop the natural flow of nature.When making a stump garden, how far do you bury the stumps? How do I keep the stumps from rotting?
We never buried the stump any further than we needed to have enough soil to support whatever plant we were going to put overtop.





Also, you can't stop the stump from rotting and you don't really need to since the rotting will be very slow (like maybe fractions of an inch per year) since it is underground. You aren't going to wake up one day with a collapsed garden.