Cat peeing on front door Help

[shoofly]

We have an ongoing issue with a neighbours cat.
We have a neutered boy cat 🐈 about 4 years old. We got him when he was 1ish from a rescue. He's a beautiful boy but occasionally is in fights with a black and white cat which lives somewhere locally. For quite some time there's been cat pee up the outside of our front door, and on doorstep and mat.
I spoke to a friend who said it was probably our cat spraying and marking his territory?

I just kept cleaning it up but this morning I could hear cat scratching at front door (claws on door mat) I opened the door to a huge puddle as this black and white bugger strode off down the drive! We can't keep him out of our garden (kids have chased with water pistol) he will even try coming through the kitchen window. Meanwhile our big soft lump of a cat has come home with a scratch on his nose and a mangled ear.

Don't know how to stop the other one terrorising ours and peeing all over the front door! Any ideas?