From Lammania Release Notes

NEW: Fighter Stalwart Defender and Paladin Defender of Siberys now have a passive threat boost when using a shield. This boost stacks with the defensive stance bonuses.

In addition, their benefits have been modified:
Fighter Stalwart Defender I
While the flesh may be weak, you place your trust in the strength of steel. This prestige enhancement increases your armor class by 1, grants +2 to your intimidate skill, increases your maximum dexterity bonus allowed by shields, and grants additional armor class and damage reduction when blocking with a shield. In addition, when you have a one handed melee weapon and shield equipped, you possess DR 2/- and your melee threat generation is increased by 25%. Also, you may expend a use of Fighter action boost to enter a defensive stance. You may possess only one prestige enhancement line at a time for each class.

Stalwart Defender: Defensive Stance
You may expend a Fighter armor boost to become a bastion of defense, gaining a +2 Competence bonus to Strength and Constitution, +10% maximum hit points, a +1 Competence bonus on all saves, and a +2 Dodge bonus to Armor Class. You also gain a 25% Competence bonus to threat generated with your melee attacks. While in this stance, you move 10% slower.

Fighter Stalwart Defender II
Your defensive mastery continues to grow. In addition to the bonuses of Stalwart Defender I, this prestige enhancement increases your armor class by 1, grants +2 to your intimidate skill, increases your maximum dexterity bonus allowed by heavy armor and shields, and grants additional armor class and damage reduction when blocking with a shield. In addition, when you have a one handed melee weapon and shield equipped, your DR is upgraded from DR 2/- to DR 4/-, and you now generate 50% additional threat with melee attacks. You may expend a use of Fighter action boost to enter a defensive stance.

Stalwart Defender II: Improved Defensive Stance
You may expend a Fighter armor boost to become a bastion of defense, gaining a +4 Competence bonus to Strength and Constitution, +15% maximum hit points, a +2 Competence bonus on all saves, and a +3 Dodge bonus to Armor Class. You also gain a 50% Competence bonus to threat generated with your melee attacks. While in this stance, you move 10% slower.

Fighter Stalwart Defender III
Your defensive mastery is complete. In addition to the bonuses of Stalwart Defender I and II, this prestige enhancement increases your armor class by 1, grants +2 to your intimidate skill, increases your maximum dexterity bonus allowed by medium or heavy armor and shields, and grants additional armor class and damage reduction when blocking with a shield. In addition, when you have a one handed melee weapon and shield equipped, your DR is upgraded from DR 4/- to DR 6/-, and you now generate 75% additional threat with melee attacks. You may expend a use of Fighter action boost to to enter a defensive stance.

Stalwart Defender III: Superior Defensive Stance
You may expend a Fighter armor boost to become a bastion of defense, gaining a +6 Competence bonus to Strength and Constitution, +20% maximum hit points, a +3 Competence bonus on all saves, and a +4 Dodge bonus to Armor Class. You also gain a 75% Competence bonus to threat generated with your melee attacks. While in this stance, you move 10% slower.

And for the Paladins:

Paladin Defender of Siberys I
Protecting the weak from the depredations of the strong, you become a paragon of defense. This prestige enhancement grants you 2 additional Turn attempts, additional armor class when blocking with a shield, increases the maximum dexterity bonus allowed by tower shields by 1, and grants the ability to enter a defensive stance or to create a Magic Circle Against Evil effect. When using a shield, you generate 25% additional threat from all sources. You may possess only one prestige enhancement line at a time for each class.

Defender of Siberys: Defensive Stance
You may expend a Paladin armor boost to become a bastion of defense, gaining a +2 Sacred bonus to Strength and Constitution, +10% maximum hit points, a +1 Sacred bonus on all saves, and a +2 Dodge bonus to Armor Class. You also gain a 25% Sacred bonus to threat generated with your melee attacks. While in this stance, you move 10% slower.

Paladin Defender of Siberys II
Protecting the weak from the depredations of the strong, you continue your training as a paragon of defense. This prestige enhancement grants you an additional Lay on Hands use per rest, and further increases the maximum dexterity bonus allowed by tower shields and heavy armor by an additional 1. When using a shield, you now generate 50% additional threat from all sources. You also gain the ability to enter an improved defensive stance or to produce a Mass Shield of Faith effect.

Defender of Siberys II: Improved Defensive Stance
You may expend a Paladin armor boost to become a bastion of defense, gaining a +4 Sacred bonus to Strength and Constitution, +15% maximum hit points, a +2 Sacred bonus on all saves, and a +3 Dodge bonus to Armor Class. You also gain a 50% Sacred bonus to threat generated with your melee attacks. While in this stance, you move 10% slower.

Paladin Defender of Siberys III
Protecting the weak from the depredations of the strong, you continue your training as a paragon of defense. This prestige enhancement increases the strength of all of your defensive auras, and further increases the maximum dexterity bonus allowed by tower shields and medium or heavy armor by an additional 1. When using a shield, you now generate 75% additional threat from all sources. You also gain the ability to enter a superior defensive stance or to defy your enemies in a glorious stand against evil.

Defender of Siberys III: Superior Defensive Stance
You may expend a Paladin armor boost to become a bastion of defense, gaining a +6 Sacred bonus to Strength and Constitution, +20% maximum hit points, a +3 Sacred bonus on all saves, and a +4 Dodge bonus to Armor Class. You also gain a 75% Sacred bonus to threat generated with your melee attacks. While in this stance, you move 10% slower.
The movement rate increases are much welcome, and I think will open these up for more use across the board.

Thoughts?