I have a 5 year old cocker spaniel and a year old irish setter. They fight approx once every two to three weeks. Each time the fight is increasingly nasty. Today the fight was really awful, the setter was choking the spaniel and she nearly killed her. Despite being yelled at, hit, and dragged apart the fight went on and on.
The spaniel is very possessive of me and is dominant, this fight was over food, but they have fought over me before. The setter is generally very easy going and sweet natured. I would hate to rehome either of them, but this was awful and frightening.
ANy advice?
 

Unfortunately once two bitches fall out they very rarely are able to live in harmony together again. Sad though it is, I think your only option is to rehome the younger bitch because she's more likely to attract a good home.

Personally if you can't keep them apart I would rehome one, this is only going to end in total disaster and I wouldn't wish that on anyone.

The setter nearly killed your spaniel this time, next time she may succeed, don't think for a moment she won't try. I agree with JG that rehoming of the setter is the kindest and safest option. It will break your heart but imagine how much worse you will feel if you end up with a dead dog. I am so sorry that I cannot be more positive, but you say yourself that every fight has got worse and this will continue.

>ANy advice?

A resounding YES.  This is a disaster waiting to happen.  Males fight to breed.  Females fight to breathe.  Your Cocker will end up dead. 

Being yelled at, hit, and dragged apart will not work.  REHOME one fast.

Sorry to hear this but the old adage of "dogs fight to breed, bitches fight to breathe" holds true
in all cases that I've known of. Bitches once they've started to fight will not 'forget'.

Unless you have the capability and set up at home that neither dog will be able to meet or be in the garden
at the same time. That everyone in the house understands this and that at no time will any doors etc be left unlatched
or dog gates left open etc.

But even the above scenario can be very stressful on the humans and the dogs especially if they both want to be with you.
Or the above may not be suitable if you have kids as accidents can happen and what if a door/gate is left open unintentionally
and a fight breaks out and you aren't at home.

Most owners come to see that the kindest thing is to rehome one of the pair. You may find it easiest to rehome the youngest
dog through either their breeder (if reputable, they will try and help rehome/take back) or a breed rescue.

I know it's probably not what you want to hear

If you search this forum for fighting bitches you will see many such threads and the advice is the same in most cases.

Bitches fight less often, but when they do ti is more seriously, they mean to cause damage not massage their egos/status as do the males.

Agree with all the others, I had 2 fighting males and that was bad enough. Unless you can absolutely guarantee you can keep them separately and still give them individual time and attention, and this could be for another 8-10 years, you are best rehoming one, I'm afraid. :-(

I had to rehome a bitch last year, broke my heart. I went to breed rescue, it was the best thing I did, we still miss her but they rehomed her two days later.She has got a wonderful life with a active retired couple who also have a male dog. Settled down very quickly and they love her to bits.
The bitch that stayed here is back to her fun loving old self. We didn't notice the stress she was under, all the fighting started after the younger bitch was spayed.one was 5 and the other 3 they had been great friends.
I hope I never have to go through girls fighting again the most terrifying thing I have ever seen. So please rehome before one is dead.

Echo all of the above. Once bitches fall out, that tends to it the end of the relationship. I know someone who had a couple of bitches fall out. It was horrendous. She couldn't ( or I should say wouldn't) rehome one of them and until one of them died of old age, life was awful. Everyone terrified of opening doors in case they let one of the dogs out. One upstairs and one downstairs, stair gates, locks on doors becuase one was a big dog (the other was a cocker actually) and they couldnt relax in case it opened the door. The whole house was TENSE. She would never go through it again and would never have a couple of bitches again in case they fell out.
I  also know someone who had to rehome one of his westies. the two bitches lived quite happily for ages then for no real reason, fell out and it just got worse and worse until he feared for their lives.