Although Jin now possessed advanced Golems and competent soldiers at his disposal, he did not think of discounting standard military defences. This was primarily because the first few hundred metres of the entrances were restricted. He was not able to fill it with clay statues and it sort of bothered him to the point of mild paranoia.
Moloch explained to him that it was an open ground designated by the Dungeon Cave itself for the invading armies to assemble. Because of this, it prompted the dungeon supplier that he might potentially lose the element of surprise of getting the clay statues to attack on sight against any invading armies.
The Dungeon Core had affirmed that the few hundred metres of the entrance were not under its jurisdiction which the System had no way to tweak the rules of the Dungeon Core. Therefore it was unable to allow Jin and his minions to place any personal property in the open area.