Customizing django admin

gistfile1.py

# models.py

from django.db import models
from django.contrib.sites.models import Site

class DomainField(models.TextField):
    def valdiate(self, value):
        " DNS domain names are always blah.something."
        super(DomainField, self).validate(value)
        if len(value.split('.')) < 2:
           raise ValidationError

    default_error_message = {
        'invalid': (u'Enter a valid domain with at least a dot (.), unicode allowed.'),
    }

class CustomSite(Site):

    domain = DomainField(help_text="This is the customer's domain that is to be accelerated.")
    enabled = models.BooleanField(help_text="This controls whether the varnish site is actually enabled.",default=True)


# end of models.py



# admin.py

from models import CustomSite
from django.db import models
from django.contrib import admin
from django.contrib.sites.admin import SiteAdmin
from django.contrib.sites.models import Site

class CustomSiteAdmin(SiteAdmin):
    pass

admin.site.unregister(Site)
admin.site.register(CustomSite, CustomSiteAdmin)

# end of admin.py

Fairly broken :(