has_shortcode() – how to detect nested shortcode

I’m using has_shortcode() to detect a shortcode, it works but not at all. If I put this specified shortcode inside another one the has_shortcode() function stops working.

has_shortcode( $post->post_content, 'slider' )

For example:

[2col] //left column
[slider]
[2col_next] //right column
[slider]
[/2col]

The has_shortcode() function won’t work in that case but if I use [slider] shortcode without [2col] it works perfect. This refers to every shortcode. I’m pretty sure that there’s nothing wrong with my shortcodes.

$page_id = get_queried_object_id();
$page_object = get_page( $page_id );
if ( strpos($page_object->post_content, '[/slider]') )