A cat can very easily scale a six foot vinyl fence (I'm assuming your comment about it being a foot high was a typo)) without breathing hard. So can possums, raccoons, squirrels, coyotes, skunks and most other wild critters. And some dogs. And most people.
What, exactly, are the problems you're having? What are you trying to prevent from happening, here? There are probably smarter ways of dealing with it than attempting to close off your yard.