Possible Clues:

• 'Canine trained to protect (5,3)'
• German shepherd, say
• Dud with aggro around? Yes and (hopefully!) no
• Deterrent to one who'd steal a broadsheet setter, possibly not Paisley?
• Mouthy type in Ring offers protection from boxer working on a lead in the security business
• Low-tech security device
• Mouthy type in Ring offers protection to American bully working on a lead in the security business
• Animal form of security