I really like looking up planted aquariums online and am in the process of trying to get mine started. My question is about the layout.

I understand the fore, mid, and background plant layout. But how do they keep those plants that spread like crazy in line? Take for instance dwarf baby tears (Hemianthus callitrichoides). It is an excellent foreground plant and is probably one of the first reasons why I chose to start a planted tank. Its beautiful in its spreading and carpet look. People seem to have such a handle on its growth, making avenues and paths on the gravel, it looks awesome. Do they just trim well or is it a border that they create?