Using the null to the right of the creep terrain. "1-13, 1-14," etc. as some people refer to it. Note you must create the units or move them to the null terrain, you can't just walk onto it, and that once they go on the null they can walk over any terrain. Which is why in mario kart battle 2 there are the buildings to keep the civv in: to prevent it from walking away. You can of course use locations and move back to create borders, which is the idea behind that Null bound that someone was making.