Good luck with that training jazz!
My dogs are trained. I taught them to be obedient and restrained around the chickens. The birds, for their part, were doing well. All was at peace in the hen yard for some time.
Until the fateful day when I went out to the yard and found every last one of the chickens dead. Not dismembered or ripped up as a predator does, but just dead. "Sported," as I likes to say.
In the chicken fence, INSIDE the main perimeter fence, was a nice sized hole. A dog-sized hole, carefully worked open and passage thus made.
This was done with my back turned, when I wasn't there to stop it. Unseen by me, a cauldron was brewing. For some reason unknown, the dogs took it in their head... and the deed was done, the frenzy begun. Only death was left in it's wake, an entire flock wiped out in one fell swoop. All that was left for me was the shovel work.
SO train away. Read all the dog psychology books and buy Cesar Milans DVD's. Make a deep track in the turf before the chicken yard, "teaching" those dogs of yours. Really get up a lather.
I did.
But dont turn your back on them. Ever. Like chickens, dogs are a Force of Nature.
Again, I recommend this thread on the matter:
Dealing with dogs