A breakwater.
A defensive wall or rampart.
A defense or safeguard.
Any means of defence or security.
The planking or plating along the sides of a nautical vessel above her gunwale that reduces the likelihood of seas washing over the gunwales and people being washed overboard.
To fortify something with a wall or rampart.
To provide protection of defense for something.
A stone bulwark forming a haven or harbour; a breakwater.