Final answer:
The independence rules require Anthony to implement an Ethical wall after accepting a key position at XYZ during the audit engagement.
Step-by-step explanation:
The safeguard that the independence rules require Anthony to implement after accepting a key position at XYZ during the audit engagement is B) Ethical wall. An ethical wall, also known as a Chinese wall, is a separation between audit and non-audit activities within a firm. It is designed to prevent conflicts of interest and maintain independence and objectivity in the audit process.