Get a couple of puppies as well, and raise them with the cats. It won't stop the cats from being outdore cats, but it will most certainly ensure that if you hear your cats getting into fights, you can let your dogs out, in which case your cats will have immediate backup.
My mom had two dogs, plus an alley cat that had insinuated itself into the house. If you know anything about cats, they tend to stake out their territory quite well. Because our cat had two dogs as backup, it essentially had no problems from other cats from Waterville St. down through the entire Munjoy South Apt. complex.
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