You'll probably get better advice, but this has been my experience and the approach I used.
I never "punished" Tucker for interest in our cats. Instead it was always a redirect. I didn't want him to associate anything bad with the cats but instead learn to ignore them. Whenever he was out around them, he had a leash attached so that I could quickly use "Leave it" & focus him elsewhere. When out walking, he is not allowed to focus on the neighborhood cats even for a second.
Now I allow the cats to do some of the work themselves. He is 6mo and I trust him slightly more (but for the cats benefit I'll never completely trust him or leave them unsupervised).
We are lucky. We have a very old, petite and declawed cat that has absoulutely no fear and when Tucker has tried to mess with her, she'll hiss but won't bother to get up until she's ready. Then she'll saunter slowly away while he bounces around frustrated because its no fun to chase a sauntering cat
Our young cat thinks he's a dog and handles him accordingly. If Tucker gets out of control with him (which means any physical contact), he goes to his crate for a time out because that usually means he's also on a rampage and destroying my house...
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