Surrounding the Lightning Country's flanks is water & as such there are no measures that are not taken for this country's military; boats from the port nearby patrol the waters close towards the land itself for defense purposes. What lays beyond however is of no concern to the Lightning Country, nor will they venture where they are not needed; those coming by sea will have to be prepared to be boarded for reasons as to why you enter Lightning Country waters, those who resist will be condemned enemys and delt with by force.
Naruto: Five Great Shinobi Nations
The start of the Five Great Nations and on.