Sounds like a prey drive that will not be broken, I am glad he is least okay when he is tied. If you do not want him to forever have to be tied, I think a no-cat home is going to be necessary.
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I never thought you have to get rid of the cat, just if you want Milo to be able to be untied when you are not home, Milo himself might be better off in a no-kitty home. I know Cami was there first!