Why won't my dog leave my cat alone. ..ever?

[Treksy]

Now, I will admit to being somewhat of a novice to dog ownership. But not completely inexperienced.
I adopted a dog in January from a shelter.Shes a little under 2yrs old,She is very obviously a border collie mix. She has strong herding instincts. I do understand that much.I have 2 cats and  2 children. She's great with kids and other dogs. But just ONE of my cats gets harassed. He will literally be doing nothing. Seriously sleeping or laying down and she will run to him and bite at him.it is almost constant. I feel bad for the cat! He can't do anything! He has scraped her in the nose a few times. She traps him in rooms. Won't let him sit with me. If I yell to my kids to come downstairs or something she gets up and runs to the cat as if he's the reason I'm yelling lol. Im not angry when I call my kids its usually" dinners ready" or something. She doesn't let a soul walk by this house without barking. Neighbors have complained ...and the police have actually come to see her because someone told them I moved and left my dog behind.
Shes a generally good natured dog. She's never bitten anyone she just has this aggression toward my cat.
If the cats were new to the situation Id chalk it up to that. But they were actually here first.

Any ideas?

Thanks

[lindapalm]

We too have a border collie mix, along with seven cats.  Our dog also herds the cats and nips at them when they don't move fast enough or go the direction she wants them to do.  After fourteen years I'm really surprised she hasn't gotten scratched bad, the cats will just hiss and run.  She didn't get along well with another smaller dog we used to have, and we had to keep and eye on her because she bit her once.  She is also very territorial when a stranger comes to the house.  In her younger years she would get her exercise by running ahead of my sons when they rode their ATV's, she would run for miles, but had to hitch a ride with them on the way back.  Shes old and deaf now, doesn't bark at anyone cause she doesn't hear them coming, but shes still in great shape.  My hope is that when she dies it will be while shes running, that is her favorite thing to do. Good Luck with your dog.

[Treksy]

She trains fairly easy. Ive gotten her to sit,lay down, give high fives and if i say" where's daddy?" She runs to the front door.
She has trouble with stay. She will as long as I'm looking she will but as soon as I turn she moves lol
She also is able to distinguish between types of toys"Luna, go get your ball" or rope,pig,ribs,donut etc she knows which is which. I always thought that was cool. It didn't take long to teach her that. We'd play with the new toy and I would say what it is a lot. But with this cat thing and barking I can say it till Im blue in the face lol.  

[Margot49]

Ok, I had 3 kids in less than 4 years.  You CAN do this!
I showed  dogs in Confirmation and Obedience for some years and worked and kept up with all school activities.  Now, I don't know how the hell I did that.  LOL,
Actually, did Obedience or Confirmation classes at night and "Dad' watched the kids on those nights.  Took 10-15 mins once or twice a day to work with the dog.  They do not have to be long sessions.  No kids present and worked in the back yard or in the driveway.  Reinforced commands in the house daily.  If I needed to, for control, I tethered the dog on leash to my jean!s loop.  This gives you control and you are able to reinforce a command like "No kitty. Leave it!"  
Does the dog know any commands?  Today is a good time to start by teaching Sit.  Do it on and off during the day, reward and praise!  You need to teach the dog to listen and connect with you.  When the dog sits, hold the treat up by your chin and see that the dog is looking at you.  Use a Sit/Stay command.  Be firm but don't yell.  If she breaks the sit, give the command again.  When she dies this, reward and praise!  Work on this for a few days.  You need to establish yourself as pack leader.

[Treksy]

Oh I would be heartbroken if she had to go Luna is like my 3rd child! Or should I say 4th? Im 14 weeks pregnant would really like to get this under control before we have a newborn here too

[Treksy]

I have tried the squirt bottle but what happens there is she starts growling and jumping,trying to bite the bottle. I feel its more playful than aggressive though

[Margot49]

Well, "Border Collie" are the key words in this scenario.  They are working digs and very intelligent.  Herding breeds are my favorites and I considered Border Collies years ago. Spoke with a reputable breeder and trainer and she flat out told me if I didn't have time to work that dog daily, I would have problems.  I appreciate the honest advice now.
Between the kids, the cats and the dog, you have your hands full.  Blu is right that the herding instinct is kicking in and who knows what the "mix" is.  
Your best bet is to start out with training and you have to work on that daily, if you can, sign up for a basic obedience class.  Look up NILF dog training.  Try to take some time each day to exercise the dog, even if is tossing a ball or frisbee in the yard to burn off some energy.
Not sure why it is after the one cat but try to be vigilant and you will see when the dog is going there.  Give a firm "No kitty!!!" Not sure why she is after the one cat.  It may be the way the cat looks at her. Or Leave it!" Call the dog to you and reward.  Really, your obedience training will help once the dog learns some basic commands, Sit, Stay, Down. leave it.  Takes time, consistency and patience daily.
Barking can be a tough one.  The squirt bottle can work well but doesn't faze some dogs. Worth a try.  Use a "no bark" command.Other than that, try not letting her have access to windows or doors where she can see people outside, move furniture, use baby gates, etc.
Sounds very confusing but once you get the hang of and timing of the training and commands, it will be easier.  Now Mom has to watch the kids and the dog. :-)
Hope it works out.  If not, you may have to rehome her.
Good luck

[BluCrystal]

This dog is attempting to 'herd' your children, pets, and protecting her territory by barking.  She needs to have her energies and intelligence shifted into positive directions, while not being petted or played with when she misbehaves.  You can begin with a squirt bottle of water, and use it every time she goes after the cat.  She only HAS to be outside if it's potty-time.  Try that, on a leash for control, and keep her out only to potty.  If she becomes distracted by a neighbor or a squirrel and begins pulling and barking, yell 'NO! NO! NO!' and bring her inside immediately, isolating her in one room of the house (like a bed room) for five minutes.  Five minutes because that is the amount of time a dog will associate an action with your reaction.  Any longer than that, and you are wasting your time.  Google dog training and dog behaviors for more information. - Blu