Cat fighting

[Cluckycluck]

We moved about 6 weeks ago, kept our cat in for the appropriate time and since being let out he is fighting with another cat.

Our boy is 10 and neutered. We live rurally and have a little over 5 acres so no need for the cats to even cross paths as our nearest neighbours are quite far away. Our cat always stays close to the house and the other cat is coming right up to our house to fight with him.

They've been left for 3 weeks as I assumed after a couple of fights they would have sorted territory out but it hasn't happened.

What can I do to stop this?

Well you can cat proof your garden but it sounds like another cat already claimed your property as his and your cats having none of it.

Is the other cat owned?.

Definitely can't cat proof 5 acres.

There appears to be two cats. Both look in good condition so must have homes. One is a gorgeous fluffy ginger one. Neither have collars though.

I am in no doubt that my boy is starting the fights. At the previous house he did fight once or twice but after the fights the other cats kept their distance.
My boy isn't getting injured so the fights appear to be more noise (my boy does tend to make very loud warning sounds to scare off other cats).
I obviously don't want any of the cats getting injured though.