Developers can ensure the security of smart contracts by following a multi-faceted approach. First, conduct thorough code reviews and testing to identify vulnerabilities before deployment. Second, utilize static analysis tools to identify potential issues early in the development process. Third, consider external audits by security experts who specialize in blockchain to uncover hidden vulnerabilities. Finally, implement best practices such as limiting the use of external calls, using fail-safes like circuit breakers, and continuously updating smart contracts to address emerging threats.