All, thanks a bunch for such insightful and thoughtful input on my puppy
questions. Helpful, very helpful!

I will be attempting to work with puppies individually on the
biting-legs-while-running problem as well as the being-nice-to-cats
problem. It really makes the most sense to work with them individually
as several people suggested. Yes Dean, I agree, they only learn bad
stuff from one another!

The duties I was thinking of for the puppy that is going to a farm home
are the general kind of duties Sandra describes, more all-purpose than
herding per se. But Melissa's comments got me thinking about a whole
bunch of assumptions I've made. On reflection, it does seem that in many
cases fencing the farmstead area would be pretty good insurance against
the dog getting killed on the road, and wouldn't always be too expensive
or too inconvenient for all farms.

Sandra has good points about the need for dogs to be outside at night to
protect livestock and poultry. My sister just had her first raccoon
attacks on poultry and that seems to be correlated with the only time
their dog didn't have access to the chicken coop in many years. It is
practically impossible to keep the chicken coop tight enough to prevent
weasel, mink, or raccoon from getting in if they really want to. The
presence of dogs seems to make the predators stay away.

My puppy's future home is a dairy farm, and no poultry or small
livestock (except calves) so predators are not really a serious concern
in this case. But this farm and other farms in the area have had thefts
of equipment from machine sheds and barns over the years, and everybody
says it only happens when there is no dog around. So watchdog barking is
a primary future duty of this puppy. I think they could probably fence
the whole large farmyard area and leave the dog loose out there at
night, but they may not see that as a practical idea.

The other future duties of this puppy will be bull deterring, and rat
killing. The former mainly requires the dog to be right with a person at
all times when that person is working around the cattle and to bark at
the bull if it approaches and do something distracting if the barking
isn't enough. Usually barking is enough but the aging ACD they now have
will nip the bulls heels for good measure. Why on earth a 2000 lb. dairy
bull would care if such a little dog bites its heels, I can't imagine,
but they do. I guess the cattle still have the primal fear of wolves.
Anyway, that duty doesn't require the dog to have free range all the
time, and does require that the dog stick very close to the person.  Rat
killing is also done under supervision, not requiring free range; the
dogs are let into areas of the barn that are usually off-limits.

Gina