I don't think taking on the responsibility for this cats behavior is mine to deal with nor should it be. I don't force my cats on others and do the right thing by keeping them in. Being asked to pay for someone else's cat to get it to behave right in a yard it does not belong in is not right...
Good luck on talking to the owner. If they are that irresponsible, they are not even going to listen or might pretend to listen but they will do what is best for them not you. Been there and done that, it just doesn't work. My final recourse was to take the animal to animal services. They...
My neighbors cat has decided that my back yard is now his new home and my inside cats are having a fit. Unfortunately, the owner of this cat gives the same general response as most people who do not want a cat inside their house "he scratches the door to go out, he cries and keeps me awake" ...