Typically, that area will be partially enclosed by friendly shoreline, defended by naval mines, monitored by sensors, and heavily patrolled by surface, submarine, and air forces.
The Soviet Union had (and, even more so, Russia now has) limited access to the world's oceans: her northern coast is ice-bound at least the majority of the year, and access to the Atlantic requires transiting the GIUK gap; much of her eastern coast is also ice-bound and requires moderately close approaches to either Alaska or Japan; travel from her southern ports involves transiting first the Bosphorus and Dardanelles, and then either the Strait of Gibraltar or the Suez Canal.
They armed their older, noisier, and less reliable "second generation" ballistic missile submarines with shorter-range nuclear weapons and deployed them as close as possible to the United States.
To secure the bastions, they also built large numbers of Sovremennyy- and Udaloy-class destroyers, whose primary mission was anti-submarine barrier and picket patrol; furthermore, the Soviet carrier-building projects were dedicated to defense of these bastions as well rather than independent strike groups, with Moskva-class limited to anti-submarine helicopters, Kiev-class carrying VTOL fighters as well as helicopters and a sizeable array of weapons (hence the designation "aircraft-carrying cruiser"), and, finally, Kuznetsov-class "heavy aircraft-carrying cruiser" fielding fixed-wing interceptors.
The United States Navy practiced penetrating these bastions; one such attempt resulted in the 20 March 1993 collision between USS Grayling (SSN-646) and K-407 Novomoskovsk, a Delfin-class ballistic missile submarine.