diff --git a/src/bar/models.py b/src/bar/models.py
index 8d4d3b87..ce82f445 100644
--- a/src/bar/models.py
+++ b/src/bar/models.py
@@ -4,7 +4,7 @@ from utils.models import CampRelatedModel
 
 class ProductCategory(CampRelatedModel):
     name = models.CharField(max_length=255)
-    camp = models.ForeignKey('camps.Camp')
+    camp = models.ForeignKey('camps.Camp', on_delete=models.PROTECT)
 
     def __str__(self):
         return self.name
@@ -16,7 +16,11 @@ class ProductCategory(CampRelatedModel):
 class Product(models.Model):
     name = models.CharField(max_length=255)
     price = models.IntegerField()
-    category = models.ForeignKey(ProductCategory, related_name="products")
+    category = models.ForeignKey(
+        ProductCategory,
+        related_name="products",
+        on_delete=models.PROTECT
+    )
     in_stock = models.BooleanField(default=True)
 
     class Meta:
diff --git a/src/program/models.py b/src/program/models.py
index 43a0c8eb..c7e7b34b 100644
--- a/src/program/models.py
+++ b/src/program/models.py
@@ -655,7 +655,11 @@ class Speaker(CampRelatedModel):
 
 
 class Favorite(models.Model):
-    user = models.ForeignKey('auth.User', related_name='favorites')
+    user = models.ForeignKey(
+        'auth.User',
+        related_name='favorites',
+        on_delete=models.PROTECT
+    )
     event_instance = models.ForeignKey('program.EventInstance')
 
     class Meta:
diff --git a/src/shop/models.py b/src/shop/models.py
index a8d3acc7..3ec7c917 100644
--- a/src/shop/models.py
+++ b/src/shop/models.py
@@ -72,6 +72,7 @@ class Order(CreatedUpdatedModel):
         verbose_name=_('User'),
         help_text=_('The user this shop order belongs to.'),
         related_name='orders',
+        on_delete=models.PROTECT,
     )
 
     paid = models.BooleanField(
@@ -290,7 +291,8 @@ class Product(CreatedUpdatedModel, UUIDModel):
 
     category = models.ForeignKey(
         'shop.ProductCategory',
-        related_name='products'
+        related_name='products',
+        on_delete=models.PROTECT,
     )
 
     name = models.CharField(max_length=150)
@@ -311,6 +313,7 @@ class Product(CreatedUpdatedModel, UUIDModel):
 
     ticket_type = models.ForeignKey(
         'tickets.TicketType',
+        on_delete=models.PROTECT,
         null=True,
         blank=True
     )
@@ -345,8 +348,8 @@ class Product(CreatedUpdatedModel, UUIDModel):
 
 
 class OrderProductRelation(CreatedUpdatedModel):
-    order = models.ForeignKey('shop.Order')
-    product = models.ForeignKey('shop.Product')
+    order = models.ForeignKey('shop.Order', on_delete=models.PROTECT)
+    product = models.ForeignKey('shop.Product', on_delete=models.PROTECT)
     quantity = models.PositiveIntegerField()
     handed_out = models.BooleanField(default=False)
 
@@ -374,7 +377,7 @@ class EpayPayment(CreatedUpdatedModel, UUIDModel):
         verbose_name_plural = 'Epay Payments'
 
     order = models.OneToOneField('shop.Order')
-    callback = models.ForeignKey('shop.EpayCallback')
+    callback = models.ForeignKey('shop.EpayCallback', on_delete=models.PROTECT)
     txnid = models.IntegerField()
 
 
@@ -402,6 +405,7 @@ class CreditNote(CreatedUpdatedModel):
         verbose_name=_('User'),
         help_text=_('The user this credit note belongs to, if any.'),
         related_name='creditnotes',
+        on_delete=models.PROTECT,
         null=True,
         blank=True
     )
diff --git a/src/sponsors/models.py b/src/sponsors/models.py
index f1823b99..bad3655f 100644
--- a/src/sponsors/models.py
+++ b/src/sponsors/models.py
@@ -19,7 +19,7 @@ class Sponsor(CampRelatedModel):
         help_text='Name of the sponsor'
     )
 
-    tier = models.ForeignKey('sponsors.SponsorTier')
+    tier = models.ForeignKey('sponsors.SponsorTier', on_delete=models.PROTECT)
 
     description = models.TextField(
         help_text='A short description of the sponsorship'
@@ -57,6 +57,7 @@ class SponsorTier(CampRelatedModel):
     camp = models.ForeignKey(
         'camps.Camp',
         null=True,
+        on_delete=models.PROTECT,
         related_name='sponsor_tiers',
         help_text='The camp this sponsor tier belongs to',
     )
diff --git a/src/teams/models.py b/src/teams/models.py
index 4e6353d1..5599f27a 100644
--- a/src/teams/models.py
+++ b/src/teams/models.py
@@ -106,8 +106,8 @@ class Team(CampRelatedModel):
 
 
 class TeamMember(CampRelatedModel):
-    user = models.ForeignKey('auth.User')
-    team = models.ForeignKey('teams.Team')
+    user = models.ForeignKey('auth.User', on_delete=models.PROTECT)
+    team = models.ForeignKey('teams.Team', on_delete=models.PROTECT)
     approved = models.BooleanField(default=False)
     responsible = models.BooleanField(default=False)
 
@@ -132,6 +132,7 @@ class TeamTask(CampRelatedModel):
     team = models.ForeignKey(
         'teams.Team',
         related_name='tasks',
+        on_delete=models.PROTECT,
         help_text='The team this task belongs to',
     )
     name = models.CharField(
diff --git a/src/tickets/models.py b/src/tickets/models.py
index f81dc31e..31269e3b 100644
--- a/src/tickets/models.py
+++ b/src/tickets/models.py
@@ -18,14 +18,14 @@ logger = logging.getLogger("bornhack.%s" % __name__)
 # TicketType can be full week, one day. etc.
 class TicketType(CampRelatedModel, UUIDModel):
     name = models.TextField()
-    camp = models.ForeignKey('camps.Camp')
+    camp = models.ForeignKey('camps.Camp', on_delete=models.PROTECT)
 
     def __str__(self):
         return '{} ({})'.format(self.name, self.camp.title)
 
 
 class BaseTicket(CampRelatedModel, UUIDModel):
-    ticket_type = models.ForeignKey('TicketType')
+    ticket_type = models.ForeignKey('TicketType', on_delete=models.PROTECT)
     checked_in = models.BooleanField(default=False)
     badge_handed_out = models.BooleanField(default=False)
 
@@ -69,7 +69,7 @@ class BaseTicket(CampRelatedModel, UUIDModel):
 
 
 class SponsorTicket(BaseTicket):
-    sponsor = models.ForeignKey('sponsors.Sponsor')
+    sponsor = models.ForeignKey('sponsors.Sponsor', on_delete=models.PROTECT)
 
     def __str__(self):
         return 'SponsorTicket: {}'.format(self.pk)
@@ -93,8 +93,12 @@ class DiscountTicket(BaseTicket):
 
 
 class ShopTicket(BaseTicket):
-    order = models.ForeignKey('shop.Order', related_name='shoptickets')
-    product = models.ForeignKey('shop.Product')
+    order = models.ForeignKey(
+        'shop.Order',
+        related_name='shoptickets',
+        on_delete=models.PROTECT
+    )
+    product = models.ForeignKey('shop.Product', on_delete=models.PROTECT)
 
     name = models.CharField(
         max_length=100,
diff --git a/src/villages/models.py b/src/villages/models.py
index a6f8db8c..24b7685b 100644
--- a/src/villages/models.py
+++ b/src/villages/models.py
@@ -11,8 +11,8 @@ class Village(UUIDModel, CampRelatedModel):
         ordering = ['name']
         unique_together = ('slug', 'camp')
 
-    contact = models.ForeignKey('auth.User')
-    camp = models.ForeignKey('camps.Camp')
+    contact = models.ForeignKey('auth.User', on_delete=models.PROTECT)
+    camp = models.ForeignKey('camps.Camp', on_delete=models.PROTECT)
     name = models.CharField(max_length=255)
     slug = models.SlugField(max_length=255, blank=True)
     description = models.TextField(