Possible Clues:

• Perhaps a barrier is made of little stones like these
• In the kitchen the commander gets set back with stones
• Glass marbles
• There's precious little stones where an entrance is
• The commander gets set up with stones
• As the stones are around the entrance
• Set aga up for shiny stones
• A bit precious, as it's about the way in
• With an arm in the water, turned over the stones
• Stones, as it's about a barrier