You know how to push opponents back.

<php>echo “<b>Prerequisites:</b>”;</php> Str 13, Power Attack
<php>echo “<b>Benefit:</b>”;</php> When you perform a bull rush, you do not provoke an attack of opportunity from the defender. In addition, you receive a +4 bonus on checks made to bull rush a foe. You also receive a +4 bonus to your CMD whenever an opponent tries to bull rush you.
<php>echo “<b>Normal:</b>”;</php> A character without this feat provokes an attack of opportunity when attempting to bull rush a foe.