Has he been neutered? You may not have gotten round to this yet, but he will be reaching sexual maturity any time now. Male cats that are not neutered tend to get into fights with other toms. If he is neutered he should not be too much of a threat to other toms in the neighbourhood. It is the fox that would worry me. Most full grown healthy cats would be able to stick up for himself against a fox. I have only ever heard of foxes killing sick or old cats, Farm cats dont seem to have a problem with foxes. But at 5 months he is still a baby. I would hang on for a while. See what other advice you are offered. It is a dangerous world though. But life is full of risks. I hope your kitty has a long and happy life . I Iove cats !