exclude a custom field

function my_searchwp_omit_meta_key( $omit, $meta_key, $the_post ) {
  $url_meta = 'link-url';
  $url_found = strpos($meta_key,$url_meta);
  // if "link-url" is in a custom field meta key name, do not index it
  if ($url_found == true) {
    $omit = true;
  }
  return $omit;
}
add_filter( 'searchwp_omit_meta_key', 'my_searchwp_omit_meta_key', 10, 3 );