Instructions
Start a game of forge from the main menu of "Halo Reach." The level you choose doesn't matter, as all maps can hold additional bubble shields.
Turn into the forge editor by pressing up on the control pad. Armor abilities, vehicles, scenery and other items are created, deleted and moved by this tool.
Scroll to the "Armor Abilities" tab in the Forge Editor and then to "Drop Shield."
Fly around the map to locations where you wish to place the drop shields. Pressing the "A" button will place the armor ability on the cursor.
Pause the game and save the map to record the placement of the drop shields for your next firefight. The end game option finishes the game of forge and returns you to the start screen of "Halo Reach."