Sorry to hear this it's horrible I know. We had an unlucky start with cats, our first cat just keeled over and died at a year old, the second one, again a year old who never usually went as far as the main road, got run over and killed, we discovered her whilst in the car with all 3 children, she was still fairly 'whole', I got out of the car to see if she was alive and a car narrowly missed me and went over her again, it was horrific, I took the children back up the drive and went back with a shovel, it was really distressing. The children were really good and got over it quickly, we then got 2 more cats (2 in case we lost another) and 8 years later we still have both, cats are all different and your remaining one may not venture that far, the bell is a good idea my friends mum used to do that too, all the best x