private function createUniqueNumericSlug($slug)
    {
        if ($this->isNumericSlug($slug)) {
            // Extract last number and increment it
            $number = substr($slug, -1, 1);
            $number++;

            // Replace with new number
            $string = substr($slug, 0, strlen($slug) - 1) . $number;

            return $string;
        } else {
            return $slug;
        }
    }