Quote Quoting llworking
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Who believes that anyone, anywhere can stop a cat from going wherever the heck that cat wants to go? Seriously, unless a cat never goes outside, its not possible to fence a cat in or out.

He has a dog...its highly unlikely that he will attempt to keep cats from entering his property, because they will naturally shy away from it because of the dog.

I suspect that the OP is correct. That he wanted the hole closed to keep his dog and child in, not to keep her cat out.
It's possible to keep a cat where you want it. A screened in porch comes to mind, if someone wants Kitty to get air/outside scents (or a fully-fenced [including top] chain-link dog run).