I give them a hard stare
You have to stare them out - it is cat language. When you are winning, then you add a bit of hissing and move towards them. If necessary you can then move on to water/chasing/etc but you only need to do it once or twice. Then they Know that it is my territory
Then I just need to give them the look if they are thinking about coming in.
Still, you can't do anything when you are not there. I know this one now cuts through neighbouring gardens rather than mine, so I am winning.
(If you glance at them and then look away, it is 'come hither' in cat terms and they will sit on your knee, if they are that way inclined. This is why they sit on the knees of people who do not like cats
)