Pebble Underfoot

 
Prerequisite(s): Improved Trip
 
Benefit: When attempting to trip a creature at least two size categories larger than you, you gain a +4 bonus on opposed trip checks. If you fail to trip the creature, it cannot immediately attempt to trip you.
 
Special: A fighter may select Pebble Underfoot as one of his fighter bonus feats.
 
Source: Dragon Compendium