Player teleports are now monitored and (if necessary) redirected inside the border; sadly this doesn't prevent the original target chunk from being loaded/generated (which would be nice if it's outside your border), but at least the player never ends up there now for even a fraction of a second

src/com/wimbli/WorldBorder/BorderCheckTask.java

@@ -20,36 +20,49 @@ public class BorderCheckTask implements Runnable
 
 	public void run()
 	{
-//		long startTime = Config.Now();  // for monitoring plugin efficiency
 		if (server == null)
-		{
-//			Config.timeUsed += Config.Now() - startTime;  // for monitoring plugin efficiency
 			return;
-		}
 
 		Player[] players = server.getOnlinePlayers();
 
 		for (int i = 0; i < players.length; i++){
-			if (players[i] == null || !players[i].isOnline()) continue;
+			checkPlayer(players[i], null, false);
+		}
+	}
 
-			Location loc = players[i].getLocation();
-			if (loc == null) continue;
+	// set targetLoc only if not current player location; set returnLocationOnly to true to have new Location returned if they need to be moved to one, instead of directly handling it
+	public static Location checkPlayer(Player player, Location targetLoc, boolean returnLocationOnly)
+	{
+		if (player == null || !player.isOnline()) return null;
+
+		Location loc = (targetLoc == null) ? player.getLocation() : targetLoc;
+		if (loc == null) return null;
 
 		World world = loc.getWorld();
-			if (world == null) continue;
+		if (world == null) return null;
 		BorderData border = Config.Border(world.getName());
-			if (border == null) continue;
+		if (border == null) return null;
 
 		if (border.insideBorder(loc.getX(), loc.getZ(), Config.ShapeRound()))
-				continue;
+			return null;
 
-			Location newLoc = newLocation(players[i], loc, border);
+		Location newLoc = newLocation(player, loc, border);
 
-			if (!players[i].isInsideVehicle())
-				players[i].teleport(newLoc);
+		if (Config.whooshEffect())
+		{	// show some smoke and play the extinguish sound effect where the player was beyond the border
+			world.playEffect(loc, Effect.SMOKE, 4);
+			world.playEffect(loc, Effect.SMOKE, 4);
+			world.playEffect(loc, Effect.EXTINGUISH, 0);
+		}
+
+		if (returnLocationOnly)
+			return newLoc;
+
+		if (!player.isInsideVehicle())
+			player.teleport(newLoc);
 		else
 		{
-				Vehicle ride = players[i].getVehicle();
+			Vehicle ride = player.getVehicle();
 			if (ride != null)
 			{	// vehicles need to be offset vertically and have velocity stopped
 				double vertOffset = ride.getLocation().getY() - loc.getY();
@@ -59,19 +72,12 @@ public class BorderCheckTask implements Runnable
 			}
 			else
 			{	// if player.getVehicle() returns null (when riding a pig on older Bukkit releases, for instance), player has to be ejected
-					players[i].leaveVehicle();
-					players[i].teleport(newLoc);
+				player.leaveVehicle();
+				player.teleport(newLoc);
 			}
 		}
 
-			if (Config.whooshEffect())
-			{	// show some smoke and play the extinguish sound effect where the player was beyond the border
-				world.playEffect(loc, Effect.SMOKE, 4);
-				world.playEffect(loc, Effect.SMOKE, 4);
-				world.playEffect(loc, Effect.EXTINGUISH, 0);
-			}
-		}
-//		Config.timeUsed += Config.Now() - startTime;  // for monitoring plugin efficiency
+		return null;
 	}
 
 	private static Location newLocation(Player player, Location loc, BorderData border)

src/com/wimbli/WorldBorder/WBPlayerListener.java

@@ -0,0 +1,19 @@
+package com.wimbli.WorldBorder;
+
+import org.bukkit.event.player.PlayerListener;
+import org.bukkit.event.player.PlayerTeleportEvent;
+import org.bukkit.Location;
+
+
+public class WBPlayerListener extends PlayerListener
+{
+	@Override
+	public void onPlayerTeleport(PlayerTeleportEvent event)
+	{
+		if (event.isCancelled()) return;
+
+		Location newLoc = BorderCheckTask.checkPlayer(event.getPlayer(), event.getTo(), true);
+		if (newLoc != null)
+			event.setTo(newLoc);
+	}
+}

src/com/wimbli/WorldBorder/WorldBorder.java

@@ -1,5 +1,7 @@
 package com.wimbli.WorldBorder;
 
+import org.bukkit.event.Event;
+import org.bukkit.event.Event.Priority;
 import org.bukkit.Location;
 import org.bukkit.plugin.java.JavaPlugin;
 import org.bukkit.plugin.PluginDescriptionFile;
@@ -7,6 +9,8 @@ import org.bukkit.plugin.PluginDescriptionFile;
 
 public class WorldBorder extends JavaPlugin
 {
+	private final WBPlayerListener pl = new WBPlayerListener();
+	
 	public void onEnable()
 	{
 		PluginDescriptionFile desc = this.getDescription();
@@ -23,16 +27,8 @@ public class WorldBorder extends JavaPlugin
 		// our one real command, though it does also have aliases "wb" and "worldborder"
 		getCommand("wborder").setExecutor(new WBCommand(this));
 
-/*		// for monitoring plugin efficiency
-		getServer().getScheduler().scheduleSyncRepeatingTask(this, new Runnable()
-		{
-			public long startTime = Config.Now();
-			public void run()
-			{
-				Config.Log("Running for " + (int)((Config.Now() - startTime) / (60000)) + " minutes, has used total border checking time of " + Config.timeUsed + "ms.");
-			}
-		}, 1200, 1200);
-*/
+		// keep an eye on teleports, to redirect them to a spot inside the border if necessary
+		getServer().getPluginManager().registerEvent(Event.Type.PLAYER_TELEPORT, pl, Priority.Lowest, this);
 	}
 
 	public void onDisable()