Wordpress custom post type meta box into URL

I am trying to make a custom post type meta box into a field that accepts URL, so the field would contain http://

Here is what I have.

Registering the custom post type:

function custom_post_type() {

// Set UI labels for Custom Post Type
$labels = array(
    'name'                => _x( 'Adverts', 'Post Type General Name', 'westanglia' ),
    'singular_name'       => _x( 'Advert', 'Post Type Singular Name', 'westanglia' ),
    'menu_name'           => __( 'Adverts', 'westa' ),
    'parent_item_colon'   => __( 'Parent Advert', 'westa' ),
    'all_items'           => __( 'All Adverts', 'westa' ),
    'view_item'           => __( 'View Advert', 'westa' ),
    'add_new_item'        => __( 'Add New Advert', 'westa' ),
    'add_new'             => __( 'Add New', 'westa' ),
    'edit_item'           => __( 'Edit Advert', 'westa' ),
    'update_item'         => __( 'Update Advert', 'westa' ),
    'search_items'        => __( 'Search Advert', 'westa' ),
    'not_found'           => __( 'Not Found', 'westa' ),
    'not_found_in_trash'  => __( 'Not found in Trash', 'westa' ),
);

// Set other options for the Adverts Custom Post Type

$args = array(
    'label'               => __( 'adverts', 'westa' ),
    'description'         => __( 'Front page scrolling adverts', 'westa' ),
    'labels'              => $labels,
    'supports'            => array( 'title', 'editor', 'thumbnail' ), 
    'taxonomies'          => array( 'ads' ),    
    'hierarchical'        => false,
    'public'              => true,
    'show_ui'             => true,
    'show_in_menu'        => true,
    'show_in_nav_menus'   => true,
    'show_in_admin_bar'   => true,
    'menu_position'       => 5,
    'menu_icon'           => 'dashicons-slides',
    'can_export'          => true,
    'has_archive'         => true,
    'exclude_from_search' => false,
    'publicly_queryable'  => true,
    'capability_type'     => 'page',
    'register_meta_box_cb' => 'add_events_metaboxes'
);

// Registering the Adverts Custom Post Type
register_post_type( 'adverts', $args );

}

 // Call the function
 add_action( 'init', 'custom_post_type', 0 );

Then I'm adding 3 meta boxes, the last one being the URL one where I'd like to have it with htpp://

add_action( 'add_meta_boxes', 'add_events_metaboxes' );

// Add the Events Meta Boxes
function add_events_metaboxes() {
add_meta_box('wpt_advert_upper', 'Advert Upper Title', 'wpt_advert_upper', 'adverts', 'normal', 'high');
add_meta_box('wpt_advert_lower', 'Advert Lower Title', 'wpt_advert_lower', 'adverts', 'normal', 'high');
add_meta_box('wpt_advert_url', 'Advert Link URL', 'wpt_advert_url', 'adverts', 'normal', 'high');
}

// Add function for the Upper advert title field
function wpt_advert_upper() {
global $post;

// Noncename needed to verify where the data originated
echo '<input type="hidden" name="advertmeta_noncename" id="advertmeta_noncename" value="' . 
wp_create_nonce( plugin_basename(__FILE__) ) . '" />';

// Get the location data if its already been entered
$upperTitle = get_post_meta($post->ID, '_upperTitle', true);

// Echo out the field
echo '<input type="text" name="_upperTitle" value="' . $upperTitle  . '" class="adH1" />';

}

// Add function for the Lower advert title field
function wpt_advert_lower() {
global $post;

// Noncename needed to verify where the data originated
echo '<input type="hidden" name="advertmeta_noncename" id="advertmeta_noncename" value="' . 
wp_create_nonce( plugin_basename(__FILE__) ) . '" />';

// Get the location data if its already been entered
$lowerTitle = get_post_meta($post->ID, '_lowerTitle', true);

// Echo out the field
echo '<input type="text" name="_lowerTitle" value="' . $lowerTitle  . '" class="adH2" />';

}

function wpt_advert_url() {
global $post;

// Noncename needed to verify where the data originated
echo '<input type="hidden" name="advertmeta_noncename" id="advertmeta_noncename" value="' . 
wp_create_nonce( plugin_basename(__FILE__) ) . '" />';

// Get the location data if its already been entered
$advertUrl = get_post_meta($post->ID, '_advertUrl', true);

// Echo out the field
echo '<input type="text" name="_advertUrl" value="' . $advertUrl  . '" class="adUrl" />';

}

And finally saving all the data added to the fields.

function wpt_save_advert_meta($post_id, $post) {

// verify this came from the our screen and with proper authorization,
// because save_post can be triggered at other times
if ( !wp_verify_nonce( $_POST['advertmeta_noncename'], plugin_basename(__FILE__) )) {
return $post->ID;
}

// Is the user allowed to edit the post or page?
if ( !current_user_can( 'edit_post', $post->ID ))
    return $post->ID;

// OK, we're authenticated: we need to find and save the data
// We'll put it into an array to make it easier to loop though.

$advert_meta['_upperTitle'] = $_POST['_upperTitle'];
$advert_meta['_lowerTitle'] = $_POST['_lowerTitle'];
$advert_meta['_advertUrl'] = $_POST['_advertUrl'];

// Add values of $events_meta as custom fields

foreach ($advert_meta as $key => $value) { // Cycle through the $events_meta array!
    if( $post->post_type == 'revision' ) return; // Don't store custom data twice
    $value = implode(',', (array)$value); // If $value is an array, make it a CSV (unlikely)
    if(get_post_meta($post->ID, $key, FALSE)) { // If the custom field already has a value
        update_post_meta($post->ID, $key, $value);
    } else { // If the custom field doesn't have a value
        add_post_meta($post->ID, $key, $value);
    }
    if(!$value) delete_post_meta($post->ID, $key); // Delete if blank
}

}

add_action('save_post', 'wpt_save_advert_meta', 1, 2); // save the custom fields


  add_action('do_meta_boxes', 'change_image_box');
  function change_image_box()
 {
remove_meta_box( 'postimagediv', 'adverts', 'side' );
add_meta_box('postimagediv', __('Advert Image'), 'post_thumbnail_meta_box', 'adverts', 'normal', 'high');
 }

Sorry it's so long, thought someone might need everything to best advise. Hope someone can help, never done a custom post type before :/

Geoff