How do I get rid of the aggression?

They make medicine that you spray in your dog's water specifically for aggression. Apparently they drink it and it's supposed to calm them down so they aren't so aggressive. I've never actually used it so I can't vouch for it but if your dogs are that bad it may be worth a try.

Finding the reason is a good start. Learning to read their body language and what it means helps a lot, though not easy for everyone to do. Consult a behaviorist and then a trainer, or one who may do both. If you have ever watched the Dog Whisperer or read any of his books it will give you an insite on how dogs think and how to stop unwanted behavior. Then when you train your dogs it will make more sense to you. They have a reason for what they do,you just need to find what it is and communicate to them in their language that you don't like it and they need to stop. To me shock collars are only to be used in cases where a dog is doing something very dangerous like car chasing, and is only used once or twice until they get the idea that the "car" is doing it and they stop. It's not for everyday training. You will find touching a dog to get his attention and snap him out of a frenzy is the only way to stop them once they get out of control NOT hitting but a firm touch. It really works.

I never knew border collies to be aggressive, when I rescued my Black Lab when I got her home she acted crazy, when she saw people & dogs I took her to a behaviorist, I wasn't about to bring her back to death row, she had lived outside for 8 + yrs and then owners thought she was to old to waste money on at a Vet., they were getting a pup, will probably do the same to a pup, the on;y thing wrong with Annie besides a multitude of health problems, worms, ear infection, thyroid problem, which you should have your Vet do blood work for, it affects just about everything including personality, she is on solixine, 2 x a day not expensive well 2yrs later Annie is almost perfect, she's great with people still iffy with dogs till she gets to know them, she was never socialized she was afraid never around allot of people that were kind to her and didn't know other dogs, so it was a combo of fear & thyroid, border collies also need a job & allot of exercise, but I never met an aggressive one and I ave been around allot of them

They say that the majority of aggression issues are fear related. I would contact a trainer in your area. We have a great one here in the Phoenix Arizona area that works with the rescue I volunteer with and adopted my boxer girl from. I will send a message with the link to his site he might be able to recommend someone in your area or direct you where to go.. Everyone I talk to and at the rescue stands by him and he has helped me out. I signed my boxer girl up for his class in October for both of our benefits and to reinforce everything I have been teaching her.

Dog aggression towards humans can be caused by different reasons. I would seriously consider working with a behaviorist or trainer to recognize the reason. Human aggressive dogs require professional help. Dog bites are no laughing matter, especially when you can be sued, lose your home owners insurance, the dog put down, etc.