Eternium is far more valuable than Gold as it is needed for constructing your armoury and HQ while Gold is used for upgrading your troops and mines. It is advised that you keep you Gold and Eternium buildings separated from each other on different sides of your base and focus on keeping your Eternium protected as this is the resource you need to upgrade your guard towers and other defenses. The best way to defend your Eternium buildings is to place your defenses in a ring around them. Even if your opponent achieves victory and your Gold is looted in the process you will at least still have your precious Eternium.