Ferocious Fetch

At 5th level, a mad dog's war beast gains Improved Trip as a bonus feat. Improved Trip: You can attempt to trip your opponent in place of a melee attack. You can only trip an opponent who is no more than one size category larger than you. If your attack exceeds the target's CMD, the target is knocked prone. If the target has more than two legs, add +2 to the DC of the combat maneuver attack roll for each additional leg it has. Some creatures — such as oozes, creatures without legs, and flying creatures — cannot be tripped. In addition, you receive a +2 bonus on checks made to trip a foe. You also receive a +2 bonus to your Combat Maneuver Defense whenever an opponent tries to trip you.