New setting "handleExploitTNTWaterlog" (default false/disabled) which, if enabled, will cause TNT which explodes in liquid to actually destroy a single adjacent block in all 6 directions. This will only apply to blocks which can be destroyed by TNT normally, specifically anything other than air, bedrock, water, lava, obsidian, and enchanting tables. The destruction of these blocks will be handled as if they had been mined, dropping the appropriate item.

TNT in water/lava doesn't normally destroy any surrounding blocks, which is usually desired behavior. That's the reason this setting is disabled by default. However, it is available because it provides a method to get through waterwalls with enough persistence, and it makes cheap (non-obsidian) TNT cannons require minor maintenance between shots. Both are useful things for my server.

src/com/massivecraft/factions/Conf.java

@@ -95,6 +95,7 @@ public class Conf
 	public static boolean handleExploitObsidianGenerators = true;
 	public static boolean handleExploitEnderPearlClipping = true;
 	public static boolean handleExploitInteractionSpam = true;
+	public static boolean handleExploitTNTWaterlog = false;
 
 	public static boolean homesEnabled = true;
 	public static boolean homesMustBeInClaimedTerritory = true;

src/com/massivecraft/factions/listeners/FactionsEntityListener.java

@@ -1,12 +1,15 @@
 package com.massivecraft.factions.listeners;
 
+import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Iterator;
 import java.util.LinkedHashSet;
+import java.util.List;
 import java.text.MessageFormat;
 import java.util.Set;
 
 import org.bukkit.Location;
+import org.bukkit.block.Block;
 import org.bukkit.entity.Creeper;
 import org.bukkit.entity.Enderman;
 import org.bukkit.entity.Entity;
@@ -14,6 +17,7 @@ import org.bukkit.entity.Fireball;
 import org.bukkit.entity.LivingEntity;
 import org.bukkit.entity.Player;
 import org.bukkit.entity.Projectile;
+import org.bukkit.entity.TNTPrimed;
 import org.bukkit.event.EventHandler;
 import org.bukkit.event.EventPriority;
 import org.bukkit.event.Listener;
@@ -127,7 +131,7 @@ public class FactionsEntityListener implements Listener
 		if (event.isCancelled()) return;
 		
 		Location loc = event.getLocation();
-		
+		Entity boomer = event.getEntity();
 		Faction faction = Board.getFactionAt(new FLocation(loc));
 
 		if (faction.noExplosionsInTerritory())
@@ -141,7 +145,7 @@ public class FactionsEntityListener implements Listener
 
 		if
 		(
-			event.getEntity() instanceof Creeper
+			boomer instanceof Creeper
 			&&
 			(
 				(faction.isNone() && Conf.wildernessBlockCreepers && !Conf.worldsNoWildernessProtection.contains(loc.getWorld().getName()))
@@ -159,7 +163,7 @@ public class FactionsEntityListener implements Listener
 		}
 		else if
 		(
-			event.getEntity() instanceof Fireball
+			boomer instanceof Fireball
 			&&
 			(
 				(faction.isNone() && Conf.wildernessBlockFireballs && !Conf.worldsNoWildernessProtection.contains(loc.getWorld().getName()))
@@ -177,38 +181,47 @@ public class FactionsEntityListener implements Listener
 		}
 		else if
 		(
+			boomer instanceof TNTPrimed
+			&&
 			(
-				faction.isNone()
+				(faction.isNone() && Conf.wildernessBlockTNT && ! Conf.worldsNoWildernessProtection.contains(loc.getWorld().getName()))
-				&&
+				||
-				Conf.wildernessBlockTNT
+				(faction.isNormal() && ( online ? Conf.territoryBlockTNT : Conf.territoryBlockTNTWhenOffline ))
-				&&
+				||
-				! Conf.worldsNoWildernessProtection.contains(loc.getWorld().getName())
+				(faction.isWarZone() && Conf.warZoneBlockTNT)
-			)
+				||
-			||
+				(faction.isSafeZone() && Conf.safeZoneBlockTNT)
-			(
-				faction.isNormal()
-				&&
-				(
-					online ? Conf.territoryBlockTNT : Conf.territoryBlockTNTWhenOffline
-				)
-			)
-			||
-			(
-				faction.isWarZone()
-				&&
-				Conf.warZoneBlockTNT
-			)
-			||
-			(
-				faction.isSafeZone()
-				&&
-				Conf.safeZoneBlockTNT
 			)
 		)
 		{
-			// we'll assume it's TNT, which needs prevention
+			// TNT which needs prevention
 			event.setCancelled(true);
 		}
+		else if (boomer instanceof TNTPrimed && Conf.handleExploitTNTWaterlog)
+		{
+			// TNT in water/lava doesn't normally destroy any surrounding blocks, which is usually desired behavior, but...
+			// this change below provides workaround for waterwalling providing perfect protection,
+			// and makes cheap (non-obsidian) TNT cannons require minor maintenance between shots
+			Block center = loc.getBlock();
+			if (center.isLiquid())
+			{
+				// a single surrounding block in all 6 directions is broken if the material is weak enough
+				List<Block> targets = new ArrayList<Block>();
+				targets.add(center.getRelative(0, 0, 1));
+				targets.add(center.getRelative(0, 0, -1));
+				targets.add(center.getRelative(0, 1, 0));
+				targets.add(center.getRelative(0, -1, 0));
+				targets.add(center.getRelative(1, 0, 0));
+				targets.add(center.getRelative(-1, 0, 0));
+				for (Block target : targets)
+				{
+					int id = target.getTypeId();
+					// ignore air, bedrock, water, lava, obsidian, enchanting table... too bad we can't get a working material durability # yet
+					if (id != 0 && (id < 7 || id > 11) && id != 49 && id != 116)
+						target.breakNaturally();
+				}
+			}
+		}
 	}
 
 	// mainly for flaming arrows; don't want allies or people in safe zones to be ignited even after damage event is cancelled