Prevent form resubmission on refresh

Hi,

I'm using a comment form within the perch_blog app. I can successfully post a comment, but every time the page refreshes the comment is then duplicated.

Here is my comment form:

<perch:form id="comment" method="post" app="perch_blog" class="comment_form" action="<perch:blog id="postURL" />">
    <fieldset>
       <legend>Leave a comment</legend>
        <div>
            <perch:input type="text" id="commentName" required="true" label="Name" antispam="name" placeholder="Name*"/>
            <perch:error for="commentName" type="required">Required</perch:error>
        </div>
        <div>
            <perch:input type="email" id="commentEmail" required="true" label="Email" antispam="email" placeholder="Email*"/>
            <perch:error for="commentEmail" type="required">Required</perch:error>
            <perch:error for="commentEmail" type="format">Check format of address</perch:error>
        </div>
        <div>
            <perch:input type="url" id="commentURL" label="URL" antispam="url" placeholder="Website* (https://)" />
        </div>
        <div>
            <perch:input type="textarea" id="commentHTML" required="true" label="Message" antispam="body" placeholder="Comment*" />
            <perch:error for="commentHTML" type="required">Required</perch:error>
        </div>
        <div class="submit">
            <perch:input type="hidden" id="postID" value="<perch:blog id="postID" />" />
            <perch:input type="submit" id="submitComment" value="Submit" />
        </div>
    </fieldset>
    <perch:success>
        <p>Thank you. Your comment has been submitted and will appear on the site once approved.</p>
    </perch:success>
</perch:form>

Here is my post comment template:

<perch:before>
    <hr>
    <h2 class="comment_title">Comments</h2>
   <ul class="comments listing">
</perch:before>
    <li id="comment<perch:blog id="commentID" type="hidden" />">
      <img src="//www.gravatar.com/avatar/<perch:blog id="commentEmail" type="email" label="Email" order="2" hash="md5" required="true" />?s=120&d=mm" width="60" height="60" />
      <div class="comment">
        <div class="commenter">
          <perch:blog id="commentHTML" encode="false" html="true" type="textarea" label="Message (HTML)" order="1" required="true" />
          <perch:if exists="commentURL"><a href="<perch:blog id="commentURL" type="url" label="URL" order="3" />"></perch:if>
          <div>
            <span>Posted by </span><strong><perch:blog id="commentName" type="text" label="Name" order="4" required="true" /></strong>
          </div>  
          <perch:if exists="commentURL"></a></perch:if>
        </div>
        <i class="fa fa-clock-o"></i><p rel="bookmark" class="date"><perch:blog id="commentDateTime" format="%d %B %Y " type="date" time="true" label="Date" /></p>
      </div>
    </li>
<perch:after>
  </ul>
</perch:after>

Thanks in advance for any help! J