This is a great series around grass/snow trails using render targets, hope it helps:
there is a set of links at the top, it’s a 3 part series, start at 1
if you think about it, your screen is render target, here you are rendering from a different point of view, like you might need to if you wanted to have a live security camera. the ‘target’ is essentially a texture that you can then do whatever you want to do to textures, including painting it to a screen, like a display for a security camera, or capturing depth into the scene (looking up from below the char) to capture depth to make accurate trails.
it will cost you depending on the resolution, but you can do it as much as you want, across many things, just pay the cost. It opens up a lot of possibilities.