Set Rules in model.

This is the code I have made so far.
It works but the whole if/check slug thing is ugly and I don't think it meets decent coding practices.
I don't want any check functions inside the controller. I want all check functions inside my model.
Is this the only way to make it possible?

As I've wrote this I've thought about adding a function called "function check slug()" and then call it as $this->pages_model->check_slug();

Anyways, I'd appreciate your feedback nether the less.

PHP Code:

<?php    

class Pages_model extends MY_Model {
    
    protected $_table_name = 'pages';
    protected $_primary_key = 'page_id';
    protected $_primary_filter = 'intval';
    protected $_order_by = '';
    protected $_rules = array();
    protected $_timestamps = FALSE;

    public function set_rules($method, $slug_check = false)
    {
        if($method === 'edit')
        {
            $id = $this->input->post('page_id');
            $slug = $this->input->post('slug');
            
            $page = $this->pages_model->get_by(array('page_id' => $id), TRUE);
            $check = get_object_vars($page)['slug'];
            
            if($check !== $slug)
            {
                $slug_check = '|is_unique[pages.slug]';
            }            
        }

        $config = array(
            'add' => array(
                array(
                    'field' => 'title', 
                    'label' => 'Title', 
                    'rules' => 'trim|min_length[5]|required|xss_clean'
                ),
                array(
                    'field' => 'slug', 
                    'label' => 'Slug', 
                    'rules' => 'trim|min_length[5]|alpha_dash|required|xss_clean|is_unique[pages.slug]',
                ),
                array(
                    'field' => 'order', 
                    'label' => 'Order', 
                    'rules' => 'trim|numeric|required|xss_clean'
                ),
                array(
                    'field' => 'body', 
                    'label' => 'Body', 
                    'rules' => 'trim|min_length[5]|required|xss_clean'
                )
            ),
            'edit' => array(
                array(
                    'field' => 'title', 
                    'label' => 'Title', 
                    'rules' => 'trim|min_length[5]|required|xss_clean'
                ),
                array(
                    'field' => 'slug', 
                    'label' => 'Slug', 
                    'rules' => 'trim|min_length[5]|alpha_dash|required|xss_clean'.$slug_check.'',
                ),
                array(
                    'field' => 'order', 
                    'label' => 'Order', 
                    'rules' => 'trim|numeric|required|xss_clean'
                ),
                array(
                    'field' => 'body', 
                    'label' => 'Body', 
                    'rules' => 'trim|min_length[5]|required|xss_clean'
                )
            ),
        );
        $this->form_validation->set_rules($config[$method]);
    }
}