Border collie agression
Hey there, I realize this reply is a bit late but I thought I'd post it just the same. I own a bc and have many friends who have some as well. They are well known for being dog agressive especially the females. They don't seem to have the time it takes to be social all they want to do is work work work...
As for dealing with it, well don't let the bc win, keep bringing it to dog parks and register in puppy classes and agility etc...
The less it will see other dogs the more agressive it will get.
Also, try to let it meet other dogs on it's own terms, that is don't force the issue. Off leash is best because then it has the option of leaving if it wants to. Also, my bc can only be around other dogs if she has a job to do, like fetching a ball, then she has a focus and other dogs are just an unpleasant nuisance that she has to work around, no ball means she has to think and worry about these dogs and that's when she gets nasty.
Most bc's have been bred for centuries to have low bite reflexes, or else the sheep would be wounded all the time, which is good for us, that is why they tend to nip and not bite.
I tend to let my bc tell off other dogs just because she is 7 now and has never "bitten" a dog, but she will snap and warn them off, if the other dog doesn't understand I'll leave the area (just to be safe, she has never bitten but there is always that 1st time that I don't want to occur!)
So, there is tons of info out there on the net about bc's and the best ones are often on the bc rescue sites, because they have to deal with the real situations of dogs being dumped because of their heritage which is quite sad.
Hope this answers some questions,
if you have any specific ones please let me know.