diff --git a/shiftregister/app/models.py b/shiftregister/app/models.py
index ea3931c..70fc6ff 100644
--- a/shiftregister/app/models.py
+++ b/shiftregister/app/models.py
@@ -155,9 +155,15 @@ class ShiftRegistration(models.Model):
     def __str__(self):
         return f"{self.helper.name}: {self.shift}"
 
+    def is_pending(self):
+        return self.state == self.RegState.REGISTERED
+
     def is_checked_in(self):
         return self.state == self.RegState.CHECKED_IN
 
+    def is_withdrawn(self):
+        return self.state in (self.RegState.CANCELED, self.RegState.FAILED)
+
 
 class Message(models.Model):
     # remove limit and send long messages in multiple messages?
diff --git a/shiftregister/team/templates/molly_guard.html b/shiftregister/team/templates/molly_guard.html
new file mode 100644
index 0000000..b531af1
--- /dev/null
+++ b/shiftregister/team/templates/molly_guard.html
@@ -0,0 +1,12 @@
+{% extends "base.html" %}
+
+{% block title %}Helfer*in wirklich sperren?{% endblock %}
+
+{% block content %}
+<h3 class="title">Helfer*in wirklich sperren?</h3>
+<form method="POST">
+    {% csrf_token %}
+    <button class="button is-danger is-small" type="submit">Schicht als "nicht angetreten" markieren und Helfer*in sperren</button>
+</form>
+<a class="button mt-3" href="{% url 'team:shift' reg.shift.pk %}">Zurück</a>
+{% endblock %}
diff --git a/shiftregister/team/templates/shift_detail.html b/shiftregister/team/templates/shift_detail.html
index 3932909..7dc2334 100644
--- a/shiftregister/team/templates/shift_detail.html
+++ b/shiftregister/team/templates/shift_detail.html
@@ -27,16 +27,17 @@
     <div class="column is-one-quarter">
         <div class="box">
             <div class="is-flex is-align-items-center is-justify-content-space-between mb-2">
-                <a class="is-size-4" href="{% url 'team:helper' reg.helper.pk %}">{{ reg.helper.name }}</a>
+                <a class="is-size-4" href="{% url 'team:helper' reg.helper.pk %}"{% if reg.is_withdrawn %} style="text-decoration: line-through;"{% endif %}>{{ reg.helper.name }}</a>
                 <a class="button is-link is-small" href="tel:{{ reg.helper.phone }}">📞</a>
             </div>
             <div class="buttons">
-{% if not reg.is_checked_in %}
-                <a class="button is-warning is-small" href="{% url 'team:checkin' reg.pk %}">Als angekommen markieren</a><br>
-{% else %}
+{% if reg.is_pending %}
+                <a class="button is-warning is-small" href="{% url 'team:checkin' reg.pk %}">Als angekommen markieren</a>
+                <a class="button is-warning is-small" href="{% url 'team:unregister' reg.pk %}">Helfer*in abmelden</a>
+                <a class="button is-danger is-small" href="{% url 'team:mark_as_failed' reg.pk %}">Nicht angetreten</a>
+{% elif reg.is_checked_in %}
                 <button class="button is-success is-small" style="pointer-events:none;">✓</button>
 {% endif %}
-                <a class="button is-danger is-small" href="{% url 'team:unregister' reg.pk %}">Helfer*in abmelden</a>
             </div>
         </div>
     </div>
diff --git a/shiftregister/team/urls.py b/shiftregister/team/urls.py
index c76bf56..6c044a1 100644
--- a/shiftregister/team/urls.py
+++ b/shiftregister/team/urls.py
@@ -13,6 +13,7 @@ urlpatterns = [
     path("helper/<int:pk>", views.HelperDetail.as_view(), name="helper"),
     path("message/", views.bulk_message, name="bulk_message"),
     path("checkin/<int:pk>", views.checkin, name="checkin"),
+    path("mark_as_failed/<int:pk>", views.mark_as_failed, name="mark_as_failed"),
     path("remove_helper/<int:pk>", views.delete_shiftregistration, name="unregister"),
     path("incoming/", views.incoming_messages, name="incoming_messages"),
     path("incoming/<int:pk>", views.incoming_message, name="incoming_message"),
diff --git a/shiftregister/team/views.py b/shiftregister/team/views.py
index f119157..0425b2d 100644
--- a/shiftregister/team/views.py
+++ b/shiftregister/team/views.py
@@ -8,7 +8,7 @@ from django.views.generic import DetailView, ListView
 from django.views.generic.edit import FormMixin
 from django.contrib.auth.mixins import LoginRequiredMixin
 from django.contrib import messages
-from django.db import models
+from django.db import models, transaction
 from django.core.paginator import Paginator
 from .forms import BulkMessage, HelperShift, HelperMessage
 from datetime import timedelta
@@ -279,6 +279,22 @@ def checkin(request, pk):
     return redirect("team:shift", pk=reg.shift.pk)
 
 
+@login_required
+def mark_as_failed(request, pk):
+    reg = get_object_or_404(ShiftRegistration, pk=pk)
+
+    if request.method == "POST":
+        with transaction.atomic():
+            reg.state = reg.RegState.FAILED
+            reg.save()
+
+            # TODO: Mark helper as barred from further shift registrations (and delete pending existing ones)
+
+        return redirect("team:shift", pk=reg.shift.pk)
+
+    return render(request, "molly_guard.html", {"reg": reg})
+
+
 @login_required
 def delete_shiftregistration(request, pk):
     reg = get_object_or_404(ShiftRegistration, pk=pk)