I have created a meta box for a theme I am working on, it is a simple meta box with a check box for featured post. The problem is user can tick that check box for **multiple posts** in the **same category**. 

I want to disable the meta value from an old post once a new post published under that category. So basically only allow 1 post to be checked as featured on any given category. I think I should do something with 

```
delete_post_meta( $post_id, 'featured_post' );

```

but I am not sure how can I check previous posts and delete the post meta from them. Any suggestion?

**Update #1 :**

This is my meta box:

```
//FEATURED POST CHECK BOX

//ADD THE META BOX
add_action( 'add_meta_boxes', 'add_featured_slide' );
function add_featured_slide(){
    //POST TYPES TO HAVE THE CUSTOM META BOX 
    $ctptypes = array( 'post', 'page', 'your_custom_post_type' );
    foreach ( $ctptypes as $ctptype ) {
        add_meta_box( 'featured-slide', 'Featured Post', 'featured_slide_func', $ctptype, 'side', 'high' );
    }
}
//DEFINE THE META BOX
function featured_slide_func( $post ){
    $values = get_post_custom( $post->ID );
    $check = isset( $values['special_box_check'] ) ? esc_attr( $values['special_box_check'][0] ) : '';
    wp_nonce_field( 'my_featured_slide_nonce', 'featured_slide_nonce' );
    ?>
    <p>
        <input type="checkbox" name="special_box_check" id="special_box_check" <?php checked( $check, 'on' ); ?> />
        <label for="special_box_check">Feature this post?</label>
    </p>
    <?php 
}
//SAVE THE META BOX DATA WITH THE POST
add_action( 'save_post', 'featured_slide_save' );
function featured_slide_save( $post_id ){
    if( defined( 'DOING_AUTOSAVE' ) && DOING_AUTOSAVE ) return;
    if( !isset( $_POST['featured_slide_nonce'] ) || !wp_verify_nonce( $_POST['featured_slide_nonce'], 'my_featured_slide_nonce' ) ) return;
    if( !current_user_can( 'edit_post' ) ) return;
    $allowed = array( 
        'a' => array( 
            'href' => array() 
        )
    );
    // IF CHECKED SAVE THE CUSTOM META
    if ( isset( $_POST['special_box_check'] ) && $_POST['special_box_check'] ) {
        add_post_meta( $post_id, 'special_box_check', 'on', true );
    }
    // IF UNCHECKED DELETE THE CUSTOM META
    else {
        delete_post_meta( $post_id, 'special_box_check' );
    }
}

```