I don't think players can set up their own security zone without any cost. It's too difficult for attackers to consider the security zone with cost: the security zone needs to consume a lot of energy, minerals or money (credit). For example, it needs to consume 5K credit per Hour, the larger the security zone, the more resources it consumes. And the security zone can be opened or closed at any time (but there is a period of time between opening and closing). When the player wants to go offline, the security zone can be opened, so that the economic system in the game will become extremely useful, and ensure the power for the player to play later