There is only one place on Rise Of Lords where your ecus are in safety and cannot be plundered: the magic safe (chest).
To place ecus in this safe will allow you to put in security your ecus. You will be able to realize savings to buy expensive things.
You have to possess 300 000 ecus minimum to be able to put them in your safe. You can empty it when good seems to make purchases. However, to avoid to be plundered during a dismantling it is recommended to empty its safe when there are few Lords connected on the game. But, to avoid any risk, it's better to put itself in magic storm before emptying the safe. Indeed, certain Lords wait and are ready to attack you.
So, be discreet before such an operation.