Advice need on cat flap / stray cat

Roanmore

Hi, apologies in advance for the long post, I'm looking for some advise on cat flaps.

We have 3 cats, all over 3 years. 2 of them would be very much house cats, the older female was wild but over the years has come in to the house and sleeps there at night but is still very wary. Very gentle cat.

When we got the 2 lads there was a cat flap in the door from our previous cat, we always left it open for the 3 as it wouldn't work with batteries, no issue there, the 3 cats got used to it.
A feral cat came along though and started coming in and leaving spray all over the place, the smell was awful.

We got a new cat flap, Cat Mate Elite, we got the 3 cats microchipped and the vet programmed the flap.
We had fierce issues with it, it made a very loud noise when opening which frightened the cats and had a big tunnel which made them wary of it as well.

Over time the 2 house cats got use to it and started using it. The third cat never did.
Anyway, one day I saw the feral cat dead on the road so it allowed us put the cat flap back in to training mode and with some encouragement and bad weather the third cat stated using it again.

Fast forward to about 6 weeks ago, a new cat is around, it's not feral, a pet I'd say but it's not neutered. It's huge and frightens our 3.
He has discovered the cat flap and has come in. He has our house destroyed.
We started locking the cat flap at night but this has caused more issues. Our cats love being out late so we have to get up in the middle of the night and check to see if they are around. This is playing havoc with our sleep.

We thought the cat would have got the message and moved on and he did for a few days but he now comes back during the day and is so brazen he comes in when we're around.
I let the cats out yesterday morning and went up to have a shower, by the time I got back down he had come in and destroyed out hall way and kitchen, I'm not kidding when I say I identified about 9 places where he sprayed.I cleaned most of them with baking soda but have missed some as I can still get the smell.

This brings me back to the cat flap. It seems that it's forgotten our cats microchip or the chip has moved in the cats. Today I put them through and set the programmme again (easier than I thought, was expecting a scrap with all 3). However it's not working, all 3 have tried to come in tonight but no luck.
Has anybody used the RFID tags? Our cats have never worn collars, not too sure they'd like them.

We're going away in a months time, a neighbour is coming to look after the lads. She's done this the last 2 years and it worked out well. The lads had the freedom of the house and garden and were well fed.
We don't know what to do this year. We can't expect our neighbour to clean the house or come up late every night to see that they come in.

This cat is well groomed, somebody definitely owns him.

Stratvs

Can’t help you with rfid tags but we have a Sure Flap electronic flap which works off the microchip. One cat is allowed in/out others in only not out and has always worked perfectly. Noise is low, just a slight whirr when the flap lock deactivates. Easy to program and batteries last 4-5 months. The chip I think is best as tags can be lost. One of ours is a terror for losing collars.