modified
defended, guarded, safeguarded, protected, manned, garrisoned, barricaded, armed, barbed, electrified, entrenched, secured, strong, covered, strengthened, reinforced, buttressed, supported, surrounded, fortressed, walled, enclosed, stockaded, bulwarked, bastioned, armored, dug in, deeply entrenched, hidden, camouflaged, revetted, bristling with guns, supplied with antiaircraft guns, equipped with air bases, equipped with an antimissile system, equipped with an early warning system.
Antonyms open*, unprotected, unguarded.
