Stripping Special Characters out of a User Submitted Variable

Hello,

For the code below, I would like to strip apostrophes, periods, and slashes from the variable $find if the user enters them in.  How can I do that?  I would like to simply delete these characters, and not replace them with an underscore or anything like that.

Thanks in advance,

John

<div class="searchbox">
  <form action="search.php" method="post">
  <label>Enter Topic:
  <input type="text" name="find" size="55"/>
  <input type="hidden" name="searching" value="yes" />
  <input type="submit" name="search" value="Search" />
  </label>
  </form>
  </div>