Как создавать неограниченное количество закладок пользователю?

if( $_REQUEST['action'] == "plus" ) {
    $error = "";
    
    $list = explode( ",", $member_id['favorites'] );
    
    foreach ( $list as $daten ) {

        if( $daten == $id ) $error = "stop";

    }
    
    if( $error != "stop" ) {

        $list[] = $id;
        $favorites = $db->safesql(implode( ",", $list ));
        
        if( $member_id['favorites'] == "" ) $favorites = $id;
        
        $member_id['favorites'] = $favorites;
        
        $db->query( "UPDATE " . USERPREFIX . "_users SET favorites='$favorites' WHERE user_id = '{$member_id['user_id']}'" );