When wielding a rapier one-handed, you can add your Dexterity modifier instead of your Strength modifier to that weapon’s damage. The rapier must be one appropriate for your size. You do not gain this benefit while fighting with two weapons or using flurry of blows, or anytime another hand is otherwise occupied.
This small metal shield is worn strapped to your forearm. You can use a bow or crossbow without penalty while carrying it. You can also use your shield arm to wield a weapon (whether you are using an offhand weapon or using your off hand to help wield a two-handed weapon), but you take a –1 penalty on attack rolls while doing so. This penalty stacks with those that may apply for fighting with your off hand and for fighting with two weapons. In any case, if you use a weapon in your off hand, you lose the buckler’s Armor Class bonus until your next turn.
Does using a buckler count as using a hand that is 'otherwise occupied' in determining gaining the benefits from the Fencing Grace feat?