You did the right thing Run a Muck. We've had to put dogs down for health reasons, the big "C" and such. Always hard, but it is our job to take care of our animals and taking care may mean putting them down.
Dogs aren't bad, owners are. Any dog can be violent if they aren't properly trained. Any dog can be trained with the right amt of attention.
I've been slowly introducing my aussies to my chickens. My young one tried to bite one of the little ones that I held in my hand. I put him on his back with my hand to his throat. Not hard, but enough to get his attention. Now he won't even look at them when I put them in his face. Then I praise, praise, praise. My older dog I had less worries about. But, she did the same thing, twice. I did the same response, twice. I am going to take them with me when I feed and clean. And reinforce the "no mouth" command. Aussies, will hopefully start gaurding the chicks once they know what their role is.
They've done the same with our cats. The three that are ours, they protect, the strays they run off. I want this to continue.