Just learned this one the other day from someone who is exceptional at training:
find a bunch of hinds and attack them all and go out of war mode. Carry plenty of bucklers, and a weapon that does NOT check your highest weapon skill (so for a fencer use a cleaver, for a swordsman use a dagger), wear high armour, let the hinds hit you and you'll gain parry like mad. Carry plenty of bucklers, 10 should be enough. Carry plenty of bandages as the multiple hinds hitting you will eventually wear your health down.
Just buy the dagger/cleaver from an NPC as you don't want the higher damage from an exceptionally made one, you just want to gain parry. The dagger/cleaver won't take damage as you're rarely hitting with it.