This goes by our very understanding of the nature of technical debt, if you want to reduce it to a theoretical zero, it’s important to be able to diagnose inefficient processes, inelegant coding and in-built weaknesses as early as possible – with testing automation tools.
That can only happen when you try to approach 100% testing coverage, leaving no corners untouched. Instead of relying on in-house resources, it may be advisable in many cases to go for an experienced, mature external team competent in automation (through remote outsourcing or leveraging in-house teams).