Use secure coding practices: Smart contract code should be written with secure coding practices, such as following the secure coding guidelines from the Open Web Application Security Project (OWASP).
Use formal verification: Formal verification is a process of mathematically proving the correctness of the code. This is the most reliable way to ensure accuracy and reliability of a Defi smart contract.
Perform automated testing: Automated tests should be run on the smart contract with various scenarios to verify its accuracy and reliability.
Use an auditor: An independent third-party auditor can review the code and identify any potential problems or risks.
Deploy the contract in a test environment: Before deploying the Smart contract to the mainnet, it should be tested in a simulated environment to identify any issues.
Read: https://www.turnkeytown.com/smart-contract-development