Not denying that this is true with some breeds, but I have never had anything but females and always have two or three together. Never any fights and hardly even a warning "snark" either. It is just not an issue with shelties or rough collies. My shelties are high drive agility girls, too. I know one agility trainer with Aussies who has 6 females and one male and they never fight either. The rough collie breeders I know say their males won't even fight over a female in heat.
I once had a funny experience with overly polite collies when I was having lunch with my friend on her patio with all our girls (six female collies and shelties). A piece of turkey fell on the ground between all the girls and they just stood there looking at each other as if to say "Are you taking it? No, are you?" My sheltie (the smallest there) finally got fed up with the politeness and grabbed it after a few minutes.
That said, my agility friends with malinois, GSD, belgians, etc, NEVER have two females together. The b*tch fights with those breeds are legendary and bloody. It is a breed thing, though. There are plenty of breeders in my club with multiple females of Keeshonden, Italian Greyhounds, Portuguese waterdogs, etc not kept separated, while the terriers, huskies, Akitas, etc do have to be.