functions.php

<?php

add_action( 'pre_get_posts', 'cd_show_all_posts' );
/**
 * Show all posts on a specified archive page.
 * 
 * @author Carrie Dils
 * @link https://carriedils.com/genesis-archive-page/
 * @param object $query data
 *
 */
function cd_show_all_posts( $query ) {
	if( $query->is_main_query() && !is_admin() && $query->is_post_type_archive( 'courses' ) ) {
		$query->set( 'posts_per_page', '-1' );
	}
}

// Register widget area for archive ad.
genesis_register_sidebar( array(
	'id'		=> 'archive-ad',
	'name'		=> __( 'Archive Ad', 'cd' ),
	'description'	=> __( 'Use this widget area to display and add on archive pages.', 'cd' ),
) );

add_action( 'genesis_after_entry', 'cd_ad_insert' );
/**
 * Display a widget area on the archive after the 2nd post.
 *
 * Uses built in Loop counter to get the index (position) of the post currently being displayed. 
 *
 * @author Carrie Dils
 * @link https://carriedils.com/genesis-archive-page/
 */
function cd_ad_insert() {
	global $wp_query;
	
	if ( 1 == $wp_query->current_post ) {
		
		genesis_widget_area( 'archive-ad', array(
			'before' => '<div class="archive-ad">',
			'after'  => '</div>',
		) );		
	}
}