Water is the best deterrent. I have zero guilt about a soaking for them.
Zero tolerance as well. If a cat even looks as if it is coming into your garden then it has to be soaked. Got one about 2 weeks ago. Friendly little bugger. Until I coaxed it in and then emptied a bucket of water over it and then chased it with the hose pipe. Funnily enough it hasn’t been back.
I liked the idea of catching it first but I tend to go for the coaxing them in tactic first.
And before anyone gets uppity, I would be happy for anyone to do the same to my own cat