"Is it real, or is it Memorex," eh?

I've seldom seen wildish critters much affected by sounds intended to scare them although some people have good success attracting them with "prey noises." It might be worth trying - but you'd need to be there to see if it worked. And they'll probably figure out that it doesn't hurt them by the second night.

I'd be inclined to expect better results from borrowing a big dog to pee on a post near the cat door; but you'd need to refresh frequently. The two, scent + noise, might work together. Some pretty exotic "odorants" are available at sporting goods stores that people use in the attempt to repel deer etc. It should be noted that some of them repel people pretty well, with lesser effect on deer.

"Civilized 'coons" are pretty much immune to lots of things one would think would discourage them. I've seen one scamper across the hood (bonnet?) of an automobile - occupied and with engine running - to jump into the dumpster beside it.

John