diff --git a/contest/models.py b/contest/models.py
index 674b004..b7bc648 100644
--- a/contest/models.py
+++ b/contest/models.py
@@ -12,7 +12,7 @@ from .validators import CallUsernameValidator
 class Contest(models.Model):
     name = models.CharField(max_length=20)
     shortName = models.CharField(max_length=20, unique=True)
-    callQrg = models.ForeignKey("Frequency", models.SET_NULL, null=True, blank=True)
+    callQrg = models.ForeignKey("Frequency", on_delete=models.SET_NULL, null=True, blank=True)
     deadline = models.DateTimeField()
 
     qsoStartTime = models.DateTimeField()
@@ -134,7 +134,7 @@ signals.post_save.connect(checkForShadowCall, sender=User)
 
 class Band(models.Model):
     name = models.CharField(max_length=10)
-    contest = models.ForeignKey(Contest)
+    contest = models.ForeignKey(Contest, on_delete=models.CASCADE)
 
     def __str__(self):
         return self.name
@@ -145,7 +145,7 @@ class Frequency(models.Model):
     # band
     channel = models.CharField(max_length=3)
     qrg = models.DecimalField(max_digits=7, decimal_places=3)
-    band = models.ForeignKey(Band)
+    band = models.ForeignKey(Band, on_delete=models.CASCADE)
 
     note = models.CharField(max_length=50, blank=True)
 
@@ -162,11 +162,11 @@ class QSO(models.Model):
             ["owner", "call"],
         ]
 
-    owner = models.ForeignKey(User, db_index=True)
+    owner = models.ForeignKey(User, on_delete=models.CASCADE, db_index=True)
     time = models.DateTimeField(blank=True)
     call = models.CharField(max_length=20, db_index=True)
-    callRef = models.ForeignKey(User, models.SET_NULL, related_name='qsoref', null=True, blank=True, default=None)
-    band = models.ForeignKey(Band)
+    callRef = models.ForeignKey(User, on_delete=models.SET_NULL, related_name='qsoref', null=True, blank=True, default=None)
+    band = models.ForeignKey(Band, on_delete=models.CASCADE)
 
     reportTX = models.CharField(max_length=7, default=59, verbose_name='RS-S', validators=[reportValidator])
     reportRX = models.CharField(max_length=7, default=59, verbose_name='RS-R', validators=[reportValidator])
@@ -176,11 +176,11 @@ class QSO(models.Model):
                                   validators=[MinValueValidator(1), MaxValueValidator(MAX_NO_VALUE)])
 
     refStr = models.CharField(max_length=20, verbose_name="EXC")
-    ref = models.ForeignKey(Reference, models.SET_NULL, null=True, blank=True)
+    ref = models.ForeignKey(Reference, on_delete=models.SET_NULL, null=True, blank=True)
 
     remarks = models.CharField(max_length=50, blank=True, default=None)
 
-    cfmdQSO = models.ForeignKey("QSO", models.SET_NULL, null=True, blank=True, default=None)
+    cfmdQSO = models.ForeignKey("QSO", on_delete=models.SET_NULL, null=True, blank=True, default=None)
 
     CFMD_SEC = 5 * 60