I've heard that you can put tape, (sticky side out), on where ever the cat is scratching. im not sure if that is for inside or outside. but im going to try it. my aunt had cats that clawed the wall on corners, she put tape on it, and they stopped.
The pet store will have something called "BItter Apple". It is usually in the dog care aisle and comes in a spray bottle. I know it kept my dog from chewing because the taste/smell is unpleasant, but it is obviously non-toxic. i'm sure a cat would find it unpleasant as well and that may keep it away from the door.
Outside of telling the neighbor to take the cat back inside (IMHO all cats should be inside cats) I would say you need to deter the cats.
#1 Can try commercial No Scratch stuff, I tried some for my cat to stop clawing the carpeted stairs, didn't work, but each cat is different. I did notice in that and the NO CHEW spray (so they don't eat my spider plants, THAT works) that it has garlic oil in it.
#2 Cayenne pepper?
So here is my suggestion mix up some chopped garlic in a spray bottle with say vegie oil (or something with some stick to it) or maybe water, and spray it all over where the kitty is scratching. Or try garlic powder mixed with hot water to dissolve. It might smell like you are cooking spaghetti sauce but it might deter the cat. Or you can mix up some Cayenne pepper with some water (Dollar stores have big bottles for cheap) and spray on there and around. Either way, if the smell doesn't deter them, the hot stuff on their paws will, it won't hurt them but it will eventually teach them a lesson!
P.S. That reminds me! I replanted an aloe outside and my rogue kitty wants to use the soft dirt as a litter box, I'd better go get some cayenne!
Let us know if it works, would be a good Thrifty Cat deterent (although I wouldn't use this in the house like I need!)
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