Prevent mounted players from unmounting.

src/com/garbagemule/MobArena/ArenaListener.java

@@ -51,6 +51,7 @@ import org.bukkit.event.player.PlayerLoginEvent;
 import org.bukkit.event.player.PlayerQuitEvent;
 import org.bukkit.event.player.PlayerRespawnEvent;
 import org.bukkit.event.player.PlayerTeleportEvent;
+import org.bukkit.event.vehicle.VehicleExitEvent;
 import org.bukkit.inventory.InventoryHolder;
 import org.bukkit.inventory.ItemStack;
 import org.bukkit.inventory.PlayerInventory;
@@ -1176,4 +1177,19 @@ public class ArenaListener
         
         arena.playerLeave(p);
     }
+
+    public void onVehicleExit(VehicleExitEvent event) {
+        LivingEntity entity = event.getExited();
+        if (!(entity instanceof Player)) return;
+
+        Player p = (Player) entity;
+        if (!arena.inArena(p)) return;
+
+        Vehicle vehicle = event.getVehicle();
+        if (!(vehicle instanceof Horse)) return;
+
+        if (monsters.hasMount(vehicle)) {
+            event.setCancelled(true);
+        }
+    }
 }

src/com/garbagemule/MobArena/listeners/MAGlobalListener.java

@@ -8,6 +8,7 @@ import org.bukkit.event.block.*;
 import org.bukkit.event.entity.*;
 import org.bukkit.event.hanging.HangingBreakEvent;
 import org.bukkit.event.player.*;
+import org.bukkit.event.vehicle.VehicleExitEvent;
 import org.bukkit.event.world.WorldLoadEvent;
 import org.bukkit.event.world.WorldUnloadEvent;
 
@@ -309,6 +310,13 @@ public class MAGlobalListener implements Listener
             arena.getEventListener().onPlayerPreLogin(event);
         }
     }
+
+    @EventHandler(priority = EventPriority.NORMAL)
+    public void vehicleExit(VehicleExitEvent event) {
+        for (Arena arena : am.getArenas()) {
+            arena.getEventListener().onVehicleExit(event);
+        }
+    }