What do I do with my dogs that don't like each other anymore?

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I have 2 dogs, one is a black lab that I had first and then I recused a beagle. I have had them both since last spring. Well, right after Christmas they got into my stash of chocolate. After that they can't be around each other anymore. My beagle will start to bark and it sets off my lab and she will bite him and actually draws blood from him. Now, I have them tied to different corners of my room and we have to keep them apart. BUT, if I am not home and my lab slips out of her collar, then there is no blood shed. I can't figure it out. I have used muzzles also, and my lab can get her off of her head sometimes. What should I do? I tried to find a home for my beagle and no one wants him. I really don't want to get rid of either of them. Thanks.