UNSIGHTED

Just find a couple critters or whatever the little arachnid pods is called - If i recall correctly they are the first kind of enemy introduced in th game.
They have only one attack consisting of a red glow before run into character direction to hit him/her, so take your time to get their rythm and master their pattern.
Believe me, it's easier than looks like.
When you are confident enough about your parrying skills against the weakest enemy in the game just spend a couple minutes pressing B to do your parries against two or three of these little pods and the chievo will pop in no time (Just don't attack them, only parry. They will be stunned for a while, but will keep full life and repeat the same pattern attacking over and over).

Took about two minutes for me to do it after find two of these things near each other. Easier than try in the trainnig challenge where keep popping stronger enemies at each 8 successful parries or so.

A perfect guard is when after parrying a hit with the enemy is stunned.

You can get it in the central hub gym.
If you do the 100 consecutive perfect parries you will get it in the process.