diff --git a/src/Overseer.ts b/src/Overseer.ts
index e6e37920e..112a0e265 100644
--- a/src/Overseer.ts
+++ b/src/Overseer.ts
@@ -196,9 +196,17 @@ export class Overseer implements IOverseer {
 	private handleColonyInvasions(colony: Colony) {
 		// Defend against invasions in owned rooms
 		if (colony.room && colony.level >= DirectiveInvasionDefense.requiredRCL) {
+
+			// See if invasion is big enough to warrant creep defenses
 			let effectiveInvaderCount = _.sum(_.map(colony.room.hostiles,
 													invader => invader.boosts.length > 0 ? 2 : 1));
-			if (effectiveInvaderCount >= 3 || colony.room.dangerousPlayerHostiles.length > 0) {
+			let needsDefending = effectiveInvaderCount >= 3 || colony.room.dangerousPlayerHostiles.length > 0;
+
+			// Place defensive directive after hostiles have been present for a long enough time
+			let safetyData = colony.room.memory.safety;
+			let invasionIsPersistent = safetyData && safetyData.unsafeFor > 20;
+
+			if (needsDefending && invasionIsPersistent) {
 				DirectiveInvasionDefense.createIfNotPresent(colony.controller.pos, 'room');
 			}
 		}
diff --git a/src/roomPlanner/BarrierPlanner.ts b/src/roomPlanner/BarrierPlanner.ts
index 41aab4722..81ff6d663 100644
--- a/src/roomPlanner/BarrierPlanner.ts
+++ b/src/roomPlanner/BarrierPlanner.ts
@@ -133,11 +133,22 @@ export class BarrierPlanner {
 	private buildMissingRamparts(): void {
 		// Max buildings that can be placed each tick
 		let count = RoomPlanner.settings.maxSitesPerColony - this.colony.constructionSites.length;
+
 		// Build missing ramparts
-		let barrierPositions = [];
+		let barrierPositions: RoomPosition[] = [];
 		for (let coord of _.keys(this.memory.barrierLookup)) {
 			barrierPositions.push(derefCoords(coord, this.colony.name));
 		}
+
+		// Add critical structures to barrier lookup
+		let criticalStructures: Structure[] = _.compact([...this.colony.towers,
+														 ...this.colony.spawns,
+														 this.colony.storage!,
+														 this.colony.terminal!]);
+		for (let structure of criticalStructures) {
+			barrierPositions.push(structure.pos);
+		}
+
 		for (let pos of barrierPositions) {
 			if (count > 0 && RoomPlanner.canBuild(STRUCTURE_RAMPART, pos) && this.barrierShouldBeHere(pos)) {
 				let ret = pos.createConstructionSite(STRUCTURE_RAMPART);