After around 2 weeks, the home finally feels safe from the invader, SaggyPuss. I have no idea what his real name might be but he’s definitely a tom cat, an unfettered entirely un-snipped stinky tom-cat.

There is no bloody excuse in today’s world to have an un-neutered moggy running around causing smelly mayhem. Unfettered cats wander looking for mates. They pee all over everywhere to mark out their territory. They get into fights, catch STDs and generally die young. All set against free snips (local anaesthetics for the boys) from the RSPCA.

About two weeks ago I came downstairs opened the door to the living room and was met by the reek of tom cat spray. The bugger had come in through the cat flap and peed as high as possible into every corner and all along the curtains to the french doors.

My three dafties, presumably watched terrified perched on top of the piano, because that’s where I found them in the morning.

Having had two very elderly cats, we had a supply of cat urine “detergent” because the stuff requires specialist biological weapons to remove.

Cats have a high protein diet which makes their pee very concentrated. If they haven’t been snipped, then tom cats feel a need to mark out territory to assert themselves, and to re-visit and re-spray their highly concentrated pee on a regular basis. Not only the cats were traumatised at the thought.

Cat pee is a nightmare to get rid of. As it dries it forms crystals of urea acid which don’t smell, but every time it rains or gets a bit damp (this is London, so quite a lot) the crystals turn back to stinky urea. So you end up buying expensive biological detergent that effectively eats the pheromone markers in the cat pee and tries to dissolve the urea. It takes repeated soakings and it isn’t cheap.

Meanwhile you search every corner with a blue light looking for the tell-tale white-yellow glow of urine, in order to douse the walls with the cat detergent. The curtains had to be sent for dry-cleaning, after a good soak for the entire bottom quarter.

But then we were left with the conundrum of how to stop a repeat offence. Although the detergent suggests it actually repels the cat from coming back, our first post-event night made it clear that was more ambition than statement of fact. Cue blue light and more detergent into every corner.

The only answer was a new cat flap, one that would “read” our cats microchips to only allow them in or out. To be clear, a determined cat can break any cat flap by sheer scratching and heft. A microchip cat flap, like a burglar alarm, just encourages unwanted visitors to head next door.

Amazon next day delivery was required.

Cue one more day of blue light and cat pee detergent because of course stinky SaggyPuss was determined to break into the living room and my three cats were totally unable to repel the intruder.

After a while of wandering around with a blu flight and anxious sniffing of floorboards, curtains etc. you start to forget what smell you’re looking for and everything, absolutely everything including the cat detergent starts to remind you of cat pee. It’s when you’ve been out and come back in, take an anxious sniff and realise that the smell hasn’t disappeared after all that you realise you have reached cat rock bottom.

The new cat flap arrived and was unwrapped. Thanks to the useful comments on the website, I knew that the best way to introduce my chipped cats to the flap was pre-installation. The cat flap had to “learn” their microchip numbers, always assuming that they’re a compatible number. We’d lost their records (I know incompetent cat parent – sue me) so had to risk outright rejection from the start at a cost of around £80 per cat flap.

Clued in by the helpful hints, we put cat treats onto the horizontal cat flap door and let the cats eat from it like a bowl to get it to register their numbers. They were a bit freaked by the noise of the catch clicking open, but at least we were confident (sort of) that it would open for each of them.

Then came the usual DIY trauma in our house of fitting anything to something. It was supposed to be the same size as the original cat flap but it turned out not to be the same depth. Cue lots of huffing and puffing before the door was in the panel and ready for use.

Lots of cat sniffing but not much usage.

Turns out that cats have very different techniques for getting through a cat flap. The boy is a head-butter and very keen to get outside once it gets dark. We’ve never been sure why he’s so keen because he has to be the most feeble hunter ever. It is of course possible that there’s some kind of complicated double-bluff going on and the reason he rarely brings anything home is because he eats it on the way. But he’s really not that bright and certainly not very dextrous. The cat toys have to be waved about at a significantly slower pace for him to stand a chance of catching them.

So he had no problem getting in or out, once he’d got over the initial hesitation at the loud click of the catch releasing the flap.

Th youngest girl is more of a scrabbler. So her attempts to scratch open the door are not immediately successful but eventually, if inelegantly, she will shove her head close enough to trigger the catch and her paws are mostly pushing the flap at the time so she can get through.

The middle girl is just not that bothered. She’s more of a paw pusher than a head butter, and quite a cautious hunter. So she would look into the cat flap, trigger the catch and immediately pull back at the noise. Time and time again. The youngest daughter decided to “help” by judicious use of cat treats placed in the cat flap but it turns out that the cat is quite adept at reaching for cat treats paw first so that didn’t really work. After a couple of days she would just walk up to the cat flap and stretch out a paw for the treats – not quite with the programme.

Reading the instruction manual (better late than never) it instructs us to turn off the microchip recognition and just let all three use the cat flap as an open door.

But what about smelly Saggy Puss?

I would rather clear little trays each and every morning than deal with the gallons of cat pee that bugger introduced to my house in just one evening’s work. How bad can it be to just open the door and let her out each morning and evening?

So another coulee of days went by and she got used to being in at night and out most of the afternoon until eventually she made her own way in through the cat flap. And a couple of days later, she snuck out on her own as well.

It had taken quite a few days of cautious watching of her brother and sister before she could bring herself to trust in the machine, but we seem to have got there in the end.

We are safe from cat intruders, at last.