They say that you don't choose cats, they choose you. Well, in this instance it's definitely true! We have a 10 year old cat with a microchip cat flap which (in theory) only lets him through. Unfortunately our neighbour's cat has learnt how to open in from the outside, he's now constantly in our house. I've tried locking the cat flap wherever possible, but this is becoming difficult as my own cat needs to go in and out. I've shut my own cat's food in a cupboard as he's a grazer and there's often food out, the other cat has learnt how to open the cupboard door. We go out for the day and this cat is often asleep on a bed upstairs when we get back like he owns the place! He's a gorgeous cat but he's not ours and I know he's well cared for elsewhere. Any tips on what else I can do?! Things I've tried so far are chucking him out as soon as I realise he's in the house, locking the cat flap wherever possible and flicking water at him (his owner suggested this) none of these seem to phase him in the slightest.