your hyper shield is your friend. PK's seem to like to jump in, do damage and back off, heavy as they jump in will get you hit, but they'll get hit harder. If your shield isn't up, then block up, or parry up, concentrate on blocking while they are in close. counter guard break when they try it, and they all try it after a few stab attempts, after the counter, or a parry hit them with an over head light and follow up with a headbutt. they'll back out of range to get stamina back giving you time to get your shield. You can also predict their jump and swing an unstoppable heavy or charge and break their back, but only try these if your shield is up and your certain they about to try their leap, I catch so many offguard.
It can still be a hard fight if they are tough, and remember your armour won't come back if you are bleeding so concentrate on blocking and counter gb until it's 2nd nature. Get in a duel with a good one and fight duel after duel to learn your timings and their techniques, it will make you much better at dealing with them. Good luck
Shugoki main here. The main thing I use to counter peacekeepers is the magical hug of friendship. As was already stated, peacekeepers go in, stab you a few times and go out. While they can dash around quickly, they are vunerable once they dedicated themselves to a move. So what I usually do is swing the ol' painstick around in a few attempts to hit them and once they dash away I charge my attack. Now here's where you have a small window where they will usually respond with a dash. Once they do, cancel the attack into insta cuddle time.
I can't even begin to list the amount of peacekeepers who lovingly jumped into my warm embrace that way! Plus, you get to hit them afterwards if they manage to survive ^^
I only have problem with peacekeepers that spam light attacks after they take my stance off. They literally hit faster than shugoki can change guard and only way to get out is double roll backwards and that takes so much of my stamina that I will be invulnerable. Demons embrace, grab and light attacks are slower than basic light attack of peacekeeper. I think the only way to counter that is to try get lucky with the parry or try just dodge roll behind.