This conference talk explores innovative approaches to DeFi security through proactive threat prevention mechanisms. Learn how to leverage the time gap between transaction broadcasting and confirmation to counter smart contract exploits. The presentation introduces IRONDOME, a system that reconstructs attack contracts to front-run malicious transactions, effectively turning attackers' methods against them. Discover how this approach has successfully blocked 78 DeFi attack incidents, including 31 with anti-front-running strategies, and saved over $10 million in user assets across Ethereum and BNB chains. Professor Yajin Zhou, CEO of BlockSec, demonstrates practical techniques for protecting decentralized finance protocols beyond traditional code audits, offering a new defensive paradigm for blockchain security professionals.