You can have deeper dirt than most people think. The issue of anaerobic conditions still exist. The key is to utilize plants with developed root systems, swords, Cryptocoryne, Valisneria, Sagitaria and for stem options Hygrophila sp have very hardy root systems. Plants transfer oxygen from leaves down into roots and into the substrate oxygenating substrates. So, you could use an object like wood or, rocks to create a barrier to hold back the substrate and then plant the mentioned genuses to keep it healthy.
Stock lightly and carry a big filter. - I don't have aquariums. I have ecosystems in a glass box. - Hygrophilaholic and hoarder of Anubias.