diff --git a/core/models/caves.py b/core/models/caves.py
index 1155f81..91453fc 100644
--- a/core/models/caves.py
+++ b/core/models/caves.py
@@ -81,7 +81,7 @@ class CaveAndEntrance(models.Model):
 
 class Cave(TroggleModel):
     # too much here perhaps,
-    area = models.ManyToManyField(Area, blank=True)
+    area = models.ManyToManyField(Area, blank=False)
     depth = models.CharField(max_length=100, blank=True, null=True)
     description_file = models.CharField(max_length=200, blank=True, null=True)
     entrances = models.ManyToManyField("Entrance", through="CaveAndEntrance")
@@ -101,7 +101,7 @@ class Cave(TroggleModel):
     underground_centre_line = models.TextField(blank=True, null=True)
     underground_description = models.TextField(blank=True, null=True)
     unofficial_number = models.CharField(max_length=60, blank=True, null=True)
-    url = models.CharField(max_length=200, blank=True, null=True)
+    url = models.CharField(max_length=200, blank=True, null=True, unique = True)
 
     # class Meta:
     #    unique_together = (("area", "kataster_number"), ("area", "unofficial_number"))
@@ -188,9 +188,12 @@ class Cave(TroggleModel):
         return qms  # a QuerySet
         
     def kat_area(self):
-        for a in self.area.all():
-            if a.kat_area():
-                return a.kat_area()
+        try:
+            for a in self.area.all():
+                if a.kat_area():
+                    return a.kat_area()
+        except:
+            return ""
 
     def entrances(self):
         return CaveAndEntrance.objects.filter(cave=self)