Unwanted cat attention

My cat Minnie is 12 years old, neutered female.
We have lived in our house 3 years now.
A new cat has started coming around, a large long haired cat - looks a pure breed.
He has been hassling the cats in the neighbourhood, eating their food left outside, fighting with them.
Yesterday while we were out he came into our house thru the cat flap, fought with Minnie, scratched her up quite badly, sparyed urine all thru the house!

Please, what can i do to put him off coming around here?

I know he is just marking his territory and probably feels superior to Minnie and wishes to claim our home as his also.
I can squirt him with a water pistol to put him off, but that will only work if i see him every time - what about when i'm at work?
I can lock the cat flap and keep Minnie inside with a cat litter tray for now, but she loves going outside EDIT:-she has gone outside all her life.- , so i need to sort out a way to keep this new cat away from her.

I guess we need to win back her territory house for her?

i have gotten some recipes to clear up the cat spraying smell, but how can i prvent him coming around our house again?

I will try to find its owner and check if he's male and if he's been neutered, and if he's not, i guess i can ask for him to be neutered, as tomcats are more agressive and have larger territoryies than neutered males.

any advice on this problem? the internet isnt giving up great info at the moment.

EDIT: yes, keeping Minnie indoors is one solution, but i was hoping that there was something i could spray or do to make Minnie and our house less appealing to the unwanted cat?
I have heard that if you get lion urine and spray this around your property, that it puts off other domestic cats. and if humans pee outside your house, may also work? any experience of using large animal urine to scare off cats? this may also scare Minnie?
EDIT: Minnie and I are from England.

Getting him neutered would help alot, he would act nicer too after that.

I would say put a repellent down, but then I would worry about it repelling minnie.

Wait for more replies.

I know it won't stop him coming around your yard, but we have a magnetic cat flap - the one with then little magnet which you attach to your cats' collar - this trips a little latch in the cat flap so only your cat can get inside - this solved a lot of our problems (there are about 20 cats in our nearby houses!!)

Wow. Is this someone's cat? Does it look cared for? I'd not only want to invest in that magnetic cat door that was suggested, but I'd also want to find its owner and let them know what is going on. I'd hate to see your baby lose the privilege of her kitty door but you do need to think of her safety.

If its a stray, maybe taking it to be neutered would be a good idea as it sounds in heat.

Welcome to TCS - I hope someone who has more experience with these situations can help you.

If you have the funds, take him to the vet and get him neutered. Obviously if he's allowed to run free like that the owners (if he has one) don't care what he's doing.

If he has an owner you can complain and request that he be neutered and pay for the vet bills for Minnie's injury.
If he is a stray you can ask animal control to get him or catch him yourself and bring him to the shelter where he should be neutered and hopefully adopted out.
BTW, I have all my cats go outside and I DO CARE what happens to them contrary to what fluffysimba just posted.