I had a beautiful Dane bitch that was ok with cats (I had 6) but seriously dog aggressive like yours. She was obedient on a leash, didn't lunge or pull, but if another dog came running up to us it was impossible to keep her from grabbing it, and if she was off-lead all she had to do was see another dog and her aim was to kill it. She killed a schnauzer mix that ran up to us on-lead with one chomp, and seriously mauled our neighbor's pit bull (the pit incident was the owner's fault, we were in the fenced yard around our apartment building and he let his dog out to "show me his dog was tougher"-not!) I tried a muzzle, but she was miserable with it on, and didn't want to walk or even move whenever I tried it. I lived in the city, and was lucky enough to find her a home in the country where the people's previous Dane had just passed away. They had a 10 ft. fence and 6 kids, 'Tasha lived out her life with them as a happy only dog who didn't need to go out and encounter other dogs.
I also had an inveterate cat-killer, best dog I ever had except for that one problem. She was even out in our yard when our rabbits escaped and she didn't touch them, but she thought cats were food and actually consumed them. She didn't even look at them when anyone was around, but the minute no one was watching... The solution? I did without cats for 12 years.