gistfile1.php

<?php

$rules = array(
    'description' => 'required|naughtywords',
);

Validator::extend('naughtywords', function($attribute, $value, $parameters)
{
    return strpos($str, 'a***') === FALSE
});

$messages = array(
    'naughtywords' => 'The :attribute must not contain naughty words',
);

Validator::make(Input::all(), $rules, $messages);