New aggression/stalking toward one cat by another in family of four cats

Sounds like misdirected aggression to me.  He can't or thinks the dog is too big so he pounces on the one he knows he can be the strong one with.  Is the dog outside or inside?  If indoors, I would recommend keeping them as separated as possible.  Sometimes cats and dogs cannot be friends if they have not grown up together.  This is not always the case but maybe in the past, they had a bad experience with dogs that you don't know about?  Cats don't forget!   This may help somewhat.  Out of sight, out of mind.  But not entirely. 

 

I am sure everyone here will say to get Feliway plug ins.  But if you've tried the calming collar, it probably won't help much more than that.  There are medicines they can take .  Anti anxiety medicines.  I am surprised your vet hasn't offered them to you yet?  Maybe tell him/her that you've tried other things and they aren't working?  I am not an advocate for shoving pills down a pets throat but rather than give them up, I'd do that first and see if it helps. 

 

Like with humans, pills only help so much.  Keeping them separate will help.  Is is just the one male and female?  Ok, that would be easier.  Making sure they can't see the dog will be a big help, too.   Maybe sometime later, if the pills are helping, you can reintroduce them in a more calm environment.  The puppy will be more experienced with cats and the cats will be calmer.   I am sorry.  Cats usually have a hard time dealing with change but usually accept it in a reasonable time frame.  Unless something in their past has traumatized them. 

I'm sorry for the double post but I was talking to a friend this evening about how my Piper and her German Shepherd, Nala, hated eachother when they first met.  And what he did to make them get along.  (We were roomates at the time.)  It may help in your situation. 

 

Dogs and especially puppies have a tendency to be more in your face and possessive of humans and cats territorial.  If a dog/puppy is its typical self, a cat may feel confined/smothered and start lashing out.  So my suggestions in the post before still stand. 

 

You need to reintroduce them.  But, first you need to get them to associate eachother in a positive way.  Put up baby gates in a couple of entrances.  Put a pet in each of the confined areas, apart from eachother.  Get their favorite dish, I mean something they really love but maybe you rarely give them or something they've never had before that you know they'll find yummy and the most awesome thing in the world.  Put there dish by the gates, maybe a foot or so from the gate and about 2 ft from eachother.  The smell of the food and the smell of the other animal will be associated with something good. Don't jump the gun though.  Still keep them behind the gates where they can't actually get to eachother. 

 

Everyday, several times a day, go on both sides of the gate and you sit by the gate.  You talk to both in a calm and loving manner.  Petting them and telling them how good they are.  Each good interaction, with no snarling, hissing, slapping, scratching or jumping... You reward with a treat.  Soon, they will see that getting along and being calm means getting a reward. 

 

Once they are all able to be in the same room together, maybe not perfectly and not exactly best friends but comfortably coexisting and maybe giving eachother space is only half the battle.  Try playing with them together.  If they start playing together and realizing it's not so bad, but actually fun... That can lead to friendship and a harmonious home again. 

If the adoption of the dog set the cat off, then the cat is still reacting to the dog.

Some of my cats really acted out when we adopted a pair of puppies years ago. What restored the peace in the household were a number of things. Cat condos in any room where the dogs were allowed so that the cats had an escape route (not to mention more vertical territory). Child gates to keep the puppies in very specific rooms in the house so that the cats could still have their space. Most importantly was obedience training for the puppies, once they were old enough to handle it.

Dogs aren't their species and most cats don't understand them. Training the dog to put the cat higher than them in the pecking order goes a long way to relaxing the cat. My dogs are not allowed to eat the cat food on the floor. The dogs must ask to join me on the sofa if a cat is up there with me. The dogs understand the phrase "that's a kitty toy, not a doggy toy" and they drop their toys. My dogs are highly reprimanded if they happen to bump into a cat while playing. I had to do this, as my dogs are between 75 and 95 pounds and can hurt a cat if they aren't aware of them.

Dogs love to please you and those they judge as higher ranking. Place a cat above the dog in the household and both species lives better for it.

Momofmany is right...Another thing to point out is that dogs and cats have different methods of getting to know eachother and different "languages" if you will.  Here's a not unusual scenerio:  People have a cat.  They love kitty but decide to get a dog, too, they think a puppy because then the kitty can get used to it easier and it will grow up knowing kitty.  They don't take kitty with them to adopt and see the reactions.  They don't let kitty have a "say".  They bring puppy home and puppy chases and jumps all over kitty.  People laugh.  They think its cute.  What they don't realize is that the kitty sees it entirely different and like as aggression.  The kitty sees it as doggie kicking him out of his territory, literally and the humans are no longer on his side.  He has no place he feels safe any more.  He starts lashing out.  Who gets the blame?  Who's the bad one?  The cat.  Everytime.  People don't realize that they created this situation and they didn't introduce them in a controlled and safe way.  Cat isn't the problem.  Dog isn't the problem.  They just don't know how to communicate with one another.  That is why I suggested the way I suggested before.  Not saying that's what's happening here.  But, I've seen this so much.  Always the kitty that has to go if no solution is found.  So sad.  When kitty didn't do this and kitty isn't the bad guy here.  There is a lot of work to be done to get them to all coexists and live comfortably with eachother.  Only you can do it.  And you have to want to.  I hope you do.