Re: Cat trying to hurt my Alfa :(
The ultrasonics do work, I have a mains powered one from ebay, only about £20 with adapter, leave it 24/7 will also stop them using your property as a toilet.
You can also get the ultrasonics as battery powered, but a pain knowing when the batts need replacing, the one I have has a LED and
has been doing its job for over a year now, we set it on a timer as the little darlings seem to be let out at night, day time no problem my springer spaniel loves the chase,never catches anything though, just remarks his territory.
Foxes are even worse, I cought one sitting on my car roof one night
he was magnificent but did it stink, off went the dog, and away flew the fox, you can get ultrasonics for the foxes, but a much higher frequency is required they are up at the top end of the sound spectrum, then dogs, then cats then ? and down to us.
Anyway go for it the ultrasonic will serve two jobs, no cat scratches, and no digging and crapping in your gravel or soil.
Sometimes a cat will challenge the ultrasonic and try to stare it out especially the local Tom, but eventually they sod off and find a new comfort zone.