We used
https://www.amazon.com/Parmak-Energizer-Impedance-Controller-SE5/dp/B0002YUWHA/ref=sr_1_9?crid=1T4GINYDNZ6GO&keywords=fence+charger&qid=1653987901&sprefix=fence+charger,aps,182&sr=8-9 for our goats. It runs around 12,000 with everything it's hooked up to now. It's handy because it displays what it puts out instead of having to guess. I also use a fence tester (that goes up to 12,000) to verify.
If you're going to have an electric fence for something this specific - I would have at least one ground wire down low. Some folks use them for up high- say where a raccoon might scale their fence and be up off the ground. If the animal isn't touching the ground, it can't be shocked. Also - because electric chargers work by sending a pulse out every second or so- the potential exists for there to be be a no-shock contact- how and where the dog touches the fence can have an impact on whether it reacts. By making sure its body WILL be in contact with your ground wire (a wire attached to your ground rod system) AND your hot wire at the same time ups the chance of repelling the invading animal.
Special attention will have to be paid to keeping the vegetation chopped nice and low underneath- even the best charger can only do so much with a bunch of stuff touching the fence.
And of course check your local laws to make sure electric fences are permitted in your area. Also - if your chickens will ever be outside this fenced area - they can get shocked too.
I'm sorry you've had to go through this. I hate that this dog has already obliterated someone else's flock before yours. Check into your local laws - since it has already damaged someone else's livestock before what happened to yours- maybe there's a repeat offender or dangerous dog designation that applies to animals who kill livestock.