Sorry I can't really offer any advice. I had the same problem (and almost the same cost!) with a local tom cat. He came in the cat flap one day, though, and was confronted by my 5 (on their own territory & in their comfort zone) and one of the dogs!! He was such a coward - hid under the table & I had to grab him by the scruff to get him out! I stuffed him in a cat carrier & left him in the shed all day. I know that sounds cruel, but he was fine, then I just took him up to the road & let him go. He's been back a couple of times since, but hasn't been any trouble. Could be something to do with the fact that my neighbour (his owner) eventually gor him neutered, after much wrangling from me & almost falling out over it!