Hi! You can't correct him. Since he is a rescue, you don't know if he was hit or if aversive methods were used in the past. The best thing you can do is try to prevent fights by feeding your dogs separately. If they start to fight, say "NO" and immediately put him in a crate for a time out. (if he bites you, keep him on a leash so you don't have to pick him up) Repeat over and over until he learns that fighting only gets him a boring time out. Remember, he is *scared* and he is fighting over resources. You have to make sure that he knows that YOU control the resources. Ask him to sit before feeding him. Work with both of your dogs asking for a simple command and then giving them treats side by side. He can only have treats if he is kind to your other dog.
You really need to find a trainer who can work with you on clicker training and positive reinforcement rehabilitation. You need to learn to recognize "warning signals" that sometimes only last a split second. For example, Loki is afraid of big dogs and his reaction is to do a freak out bark. I've learned to not only recognize his body language when he is scared, but I know the milisecond he is going to react. This gives me the power to intervene and click/treat BEFORE he reacts. He learned that now when he sees a big scary dog he gets a treat if he doesn't bark. He also learned to LOOK AT ME (most important here) and break his stare at the other dog. He looks to me for cues. When he's out in the yard and dog walks by he would run at the dog (he's on a leash at all times) and bark. I've taught him instead to run inside. He runs inside BARKING the whole time he's running back to the house, but the bark is now more "MOM! A BIG DOG!" than "DON"T EAT ME YOU SCARY DOG"
Trust me, you can learn these things. You just need a good trainer and a good book and some practice
I'm happy to help if this sounds like what you want to do and you have questions.