Ways to keep cat out neighbors house?

[GingerPuddin]

In talking to NDN DH discovered that one of our cats has been visiting her house for food. They have 2 cats and have a cat flap. We have 3 cats so have a cat flap because otherwise we'd be constantly letting cats in and out. We also have a toddler so I think said cat has been hanging out at theirs for the peace and quiet.
We can't keep the cat locked in. Is there any way to discourage cat from going next door? If not should we offer to paid towards ND cat food bill?

Are the neighbours actively encouraging him? And how are his weight and health doing?

PS - you can tell a lot by their general attitude.

Have they asked you to do something? We had catflap invaders and even if I'd known who the cats belonged to I wouldn't have expected the owners to do something themselves. It would be a bit rich having free-range cats myself and expecting other people to control theirs! We have a microchip catflap now and no invaders.

They haven't really said that it's a problem and thinking about it their cats occasionally try to come into our house but are chased off by our cats. I guess I should just leave it unless they do complain.
Tempted to get a microchip cat flap since two of our cats prefer to run naked and always loose collars. How much do they run? Can we fit it to an existing cat flap hole? Thanks

We have a standard SureFlap which is £70 on Amazon at the moment, and there's a £10 adaptor thing if you're putting it into a glass door, or to make a wall installation look neater. Well worth it, as now only MY cats eat food in MY house, and no one is pissing on the curtains either!

We had a normal one before, fitted into the wall, and we just replaced the inside flap with the SureFlap and kept the standard one on the outside. I intend to get the bigger version when we move house though, as it's quite small compared to my cats, and the tunnel through the wall is a bit of a challenge for them!