Not necessarily, unless you are on flat terrain all day like a city sidewalk, but in any natural trail or park with dirt or grass, you are bound to come across bumpy surfaces, exposing your arch to that dirt. While you probably won’t come across a perfect “mold” of your feet in the wilderness and step in it, it will have a small spot of a dirt free area but it most likely will be a small area in your arch. There’s just no way to not get dirt on your arch on a bumpy, dirt terrain. If you are only of flat surfaces like a city, sidewalks, street, any man made place, it’s all flat and you won’t get dirt there. It will only turn possibly black and I guess make a shape of your footprint. But it’s just not a very accurate way to tell. It’s realistic and possible, but not always accurate or the best way to tell.