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Smart contract security is the most critical aspect of Web3 development. A single vulnerability can lead to millions in losses. Here are key practices from 8+ years of development experience.

1. Reentrancy Protection

Always follow the Checks-Effects-Interactions pattern:

function withdraw() external {
    uint256 balance = balances[msg.sender];  // Checks
    require(balance > 0);
    balances[msg.sender] = 0;                // Effects
    (bool ok, ) = msg.sender.call{value: balance}("");  // Interactions
    require(ok);
}

2. Use OpenZeppelin

Don't write standard contracts from scratch. Use audited OpenZeppelin libraries:

import "@openzeppelin/contracts/access/Ownable.sol";
import "@openzeppelin/contracts/security/ReentrancyGuard.sol";

3. Access Control

Use OpenZeppelin's AccessControl instead of simple onlyOwner:

• Assign different roles for different functions
• Use timelocks for sensitive operations
• Regularly audit role assignments

4. Oracle Security

Use decentralized oracles like Chainlink and implement:

• Price validation (multi-source comparison)
• Deviation threshold checks
• TWAP to prevent price manipulation

5. Regular Audits & Testing

• Write comprehensive Foundry/Hardhat test suites
• Use static analysis tools (Slither, Mythril)
• Hire third-party auditors for professional review

Security is an ongoing process. Stay updated with the latest vulnerability reports and best practices.