How can the benefit of the feat Mounted Combat be used more than once per round?

Question

The benefit of the feat Mounted Combat says

Once per round when your mount is hit in combat, you may attempt a Ride check (as a reaction) to negate the hit. The hit is negated if your Ride check result is greater than the opponent’s attack roll. (Essentially, the Ride check result becomes the mount’s Armor Class if it’s higher than the mount’s regular AC.) (Player's Handbook 98)

Is there a class feature, magic item, spell, or something else that enables a rider to employ the benefit of the feat Mounted Combat more than once per round or, ideally, any number of times per round?

Answer 1

There Are Two Abilities

Among the books and resources I have searchable access to, I find only Prestige Class features, no feats (at least none that have Mounted Combat as a prerequisite, or that mention it or the word 'negate' in the description)

Here are the prestige class features:

Aglarondan Griffonrider (Unapproachable East, p18) gets

Improved Mounted Combat (Ex): At 3rd, 5th, and 7th level, an Aglarondan griffonrider increases by one the number of Ride checks she may attempt each round to negate a hit against her mount (two times per round at 3rd, three times per round at 5th, and four times per round at 7th). The hit is negated if the griffonrider's Ride check result is greater than the attack roll.

Ashworm Dragoon (Sandstorm, p66) gets

Relentless Shield (Ex): At 4th level and higher, you can make a Ride check after any attack that successfully strikes your ashworm mount, in an attempt to negate the hit on your ashworm. Normally, the Mounted Combat feat allows you to make this attempt only once per round. See the Mounted Combat feat, page 98 of the Player's Handbook, for details. In addition, you gain a +2 bonus on Ride checks made to negate an opponent's attack roll. This ability does not extend to any other type of mount.