Can you guys share some of the checks and balances you put in place in your projects that will force rules and restriction and help make code better maintainable.

My project is a MVC/WebAPI application. It is unit testable but no unit tests ( company doesn’t want to spend resources on writing unit testing. So this is out of questions) Any other checks and balances we can put in place to minimize error and force some sort of uniformity across the code ?