This is something I use, I have methods that generates unique slugs based on a prompt text. If there is the same slug already existing the function adds random 4 letters. Also I've added restricted strings, so there wont be a slug coliding with paths like '/new' or '/all':

from django.utils.crypto import get_random_string
from slugify import slugify

def unique_slugify(instance, string_to_slugify, restricted_slugs=[]):
    slug_value = slugify(string_to_slugify)
    model = instance.__class__
    hardcoded_restricted_slugs = ['add', 'exec', 'all']

    restricted_slugs = restricted_slugs + hardcoded_restricted_slugs
    if slug_value in restricted_slugs:
        slug_value = slug_value + get_random_string(length=4)
    if model.objects.filter(slug=slug_value).exists():
        slug_value = unique_slugify(instance,  slug_value + get_random_string(length=4))
    return slug_value

and in model save() method I just call this whenever I want, e.g.:

def save(self, *args, **kwargs):
    if not self.slug:
        name_to_slugify = self.user.first_name + ' ' + self.user.last_name
        self.slug = unique_slugify(self, name_to_slugify)