You could try Tiger Balm which should act as a repellent for cats and dogs. Used some of it at home as normally have 2 dogs and 4 cats of our own about. Stopped the dogs chewing the walls by the front door. Alternatively iirc Lemon Balm is planted in india as a repellent for Tigers so should work on the humble kitty.
We have exactly the same problem at our holiday place - a stoned driveway which the neighbour's 4 cats use as a litter box when we're not here. The place stinks until we take all the cat foul out of the stones with a shovel and bin it, which is not the sort of thing you want to do to start each holiday. We had the same problem with another neighbours dog doing it on the lawn until we reported it to the dog warden last year, at which point it was captured and taken away. I'm so sick of it with the cats now that I'm going to throw down some rotten fish around the boundary when I leave here this week and let them poison themselves. I'm not interested in deterring them any more, we've tried most of the things that have been suggested in this thread. I just want the filthy things dead now.
"Returns after leaving rotten fish, to find horrid kitty diarrhoea plastered everywhere" Have fun with that
I get quite uncomfortable with people suggesting killing animals because they are fouling on their property. Hopefully that's just some internet hyperbole, because otherwise it's absolutely abhorrent.
"...and a pile of dead rotting cats, pulsating rhythmically with maggots and riddled with disease. Also it stinks of ammonia, liquid poop and very rotten fish now, as opposed to just ammonia and scoopable poop."
Speak to the neighbours? Start talking about possible costs to repair the damage to your car and they might start getting off their arse
People are intolerant nowadays unfortunately. I'll kill a member of another persons family as I am mildly inconvenienced.
I guess it's a good thing I didn't mention my initial idea of simply shooting them. Yes, I know it's cruel and I don't exactly like the idea of making them sick, but these are no longer pets. The day their owners decided to let them roam around like wild animals they stopped being pets. It's fine to do that if you live in the countryside, especially on a farm, but this is in a developed area where they're roaming and fouling all over other people's property. Yes, we spoke to the neighbours about it. No, they didn't care. Yes, we've tried humane deterrent methods. No, they didn't work. I can't walk from the front door to the car without stepping in cat ****. "Mildly inconvenienced" is an understatement. Also, they come in the house through open doors and windows during the summer time.
I think the issue is, those cats consider it their area as you're not always around since it's a holiday home. I had a similar issue when I moved in here, it had been empty for a year previous and the cats loved sun bathing and doing there business in our little court yard. The first few days I made sure to chase them off and make like I'm the alpha. After a month they rarely show themselves now, but when they do its a friendly hello and they understand their boundaries. Tabasco sauce in a spray bottle, whilst their in the act, quick spray at their back end. They'll learn quick.
So, I'm larger than a cat... I could just piss all over the place myself, drunk, obnoxious and shouty. Be cheaper, easier and my neighbours wouldn't **** with me... Not that they do now; they sure as hell won't do afterwards for fear of gypsy retribution.
Super Soaker or garden hose. Failing that, look up the Contech Scarecrow which is basically a motion-activated sprinkler. I'll say this for completeness; physically harming a person's pet is all kinds of not cool. Use science to build a humane and watery barrier between cat butts and your primroses.
Water will do just fine. Unless you're really going to buy enough Tabasco to fill a Super Soaker then risk having the spray come back and hit you in the face? Not that it's any more of a mild dipping sauce anyways. I've used water in a plant mister to train my cat not to scratch anything other than his scratching post. It works well enough. Only need to shake the bottle now and he gets the hint. Also, I have IR/NV. You're better off letting you eyes acclimatise to the night or using an IR sensor to do the work for you.
I have found that land mines usually work best. Just make sure to map out the placement for your own reference.