Good fences make good neighbors. My uncle is a rancher, so by profession he is always repairing fences. Here in my city condo, the space between one unit’s ceiling and another unit’s floor is common area. Respect of that common area is just like a fence: treat it well and you will always have good neighborly relations.
In working groups, the fence equivalent is clear roles and responsibilities. I had a colleague whose friendly wrath served as a very effective warning. When someone was messing around in her area of responsibility, she would say, “Get out of my sandbox!”