Any means of defence or security.
A defensive wall or rampart.
A defense or safeguard.
A breakwater.
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.
The defence, collectively the defenders.
The rearmost part of a force, especially a detachment of troops that protect the rear of a retreating force.