Related Clues:

• Feature of some zoos
• Alternative to a fence
• Defensive structure
• Protective ring
• Barricade
• Water-filled trench
• Refuse to release
• Persist in
• Castle's protective feature
• Barricade in ''The Star-Spangled Banner''
• Castle's protector
• Palace guard?
• Entry to a castle, maybe
• Castle part
• Detain