How do you make a undeleteable code?

Creating "undeleteable" code is not feasible, as any code can be modified or deleted by someone with sufficient access and knowledge. However, you can implement measures to make deletion difficult, such as using permissions to restrict access, employing obfuscation techniques to make the code harder to understand, or placing critical components in secure environments. Ultimately, the best approach is to focus on secure coding practices and regular backups rather than attempting to create truly undeleteable code.