respect-validation/library/Rules/LeapDate.php

<?php
namespace Respect\Validation\Rules;

use DateTime;

class LeapDate extends AbstractRule
{
    public $format = null;

    public function __construct($format)
    {
        $this->format = $format;
    }

    public function validate($input)
    {
        if (is_string($input)) {
            $date = DateTime::createFromFormat($this->format, $input);
        } elseif ($input instanceof DateTime) {
            $date = $input;
        } else {
            return false;
        }

        // Dates that aren't leap will aways be rounded
        return $date->format('m-d') == '02-29';
    }
}