Possible Clues:

• Catch people using this oft-repeated phrase quietly
• Rampant (anag.)
• Slogan presented with power is something that ensnares folk
• It can be very catchy perhaps, that word repeated quietly
• Snare for catching people
• In Hindu mystical music, quietly vamp
• What may catch trespassers, some returning to island
• Something often repeated quietly — a hidden danger?
• Novel by Sinclair Lewis
• Rampant (anag) — anti-trespasser device