How do I handle discount code misuse and fraud prevention?

As an e-commerce store owner, I'm constantly battling discount code abuse that's cutting into my profit margins. Customers are sharing codes publicly, using expired promotions, creating multiple accounts to exploit discounts, and finding creative ways to circumvent my intended promotional strategies. I need a comprehensive approach to prevent fraud, protect my revenue, and maintain the integrity of my discount campaigns while still offering genuine value to legitimate customers. What are the most effective methods to detect, prevent, and mitigate discount code misuse?