My boy is bad

Yesterday I caught Wawa in my neighbor's garden picking up a fight with the neighbor's cat. Sheesh... Ever since he was neutered, he has never gone beyond the property until yesterday. However, he was originally a stray and when I found him he was badly wounded and scarred from catfights. Is he going back to the "old days"? My neighbor is not kind to animals if they behave badly (I've heard him hit his dogs) and I am afraid for my boy.
Keeping him indoors is not an option because my other 3 (all female) are let out whenever they want and Wawa will be miserable if treated differently. Will some "jail time" be a good way to train him? It works whenever any of them misbehave.

better to be inside and temporarily miserable, then to be an outside cat and end up dead or very hurt in a figh. thats just how i see it.

Thanks! But I found a solution. I'll talk to my neighbor. His cat isn't neutered and it probably "teased" Wawa into chasing him to his territory. I know my boy is no doormat! My neighbor and I will probably put a wire fence over the wall so both our cats can't visit each other OR he better neuter his tom!

The wire fence idea sounds really good, Y.