Which country has its own ocean?

Could you please elaborate on the intriguing concept of a country possessing its own ocean? This seems to be a unique and fascinating geographical notion. Are there any specific countries that can be identified as having their very own ocean? If so, what are the defining characteristics that set these countries apart? Is this a geographical anomaly, a political construct, or a natural occurrence? Could you also provide some historical context and perhaps discuss the implications this might have for the country's economy, security, and environmental policies? I'm eager to learn more about this fascinating topic.