So here shines a nuance of the Django ORM.. when a model is saved, _all_ fields are updated for that record. This has been exposed/fixed in [Django 1.5](https://docs.djangoproject.com/en/1.5/ref/models/instances/#saving-objects) with the `update_fields` argument, but until then, it should be this:

```python
self.model.objects.filter(pk=request.instance.pk).update(accessed=datetime.now())
```

This minimizes what is being updated and prevents the `modified` timestamp from being updated.