Military men among the vigilantes recognized the headquarters on Sacramento Street as virtually indefensible in an attack by the law and order party. There was some talk of moving but in the end it was resolved to strengthen the existing building. The sewers in the area were thoroughly checked and measures taken to prevent access from them. An idea for portable barricades was offered by the French legion and suggestions were received from noted military persons from as far away as Europe. At the same time it was well known that the law and order party planned to place an artillery battery on Rincon Hill and other high points to shell the building. Plans were made to capture these batteries and all the men there. Meeting places for the assembly of the vigilantes, one at the Oriental Hotel and another at the Monumental Engine House, were agreed on. All members would wear a piece of white ribbon in the top buttonhole in the upper left lapel of his coat and use the rallying cry of “vigilantes.”
The most remarkable thing that was done was the fortification of the headquarters building on the night of June 10th that attracted thousands of spectators. A wall of course sacks, known as gunnybags, filled with sand and piled up to form a breastworks was constructed from the front corners of the building across the sidewalk and onto Sacramento Street and then ran down the street to form an enclosure. Cannon were placed at several points along this wall and there were inside platforms and openings from which musket fire could be poured on any attackers. A few small cannon were also placed on the roof of the building to counteract any plans attackers might have. While it was doubtful these defenses could have withstood a determined attack by well armed forces, they did inspire the vigilante members and for this some praise was given to Francis J. Lippett for both the idea and construction of the fortification.