No other cats have come into my garden since I got it done. Occasionally they sit on the fence on the other side of the netting, but none have been crazy enough to try jumping up and in over the netting. They cannot climb the netting, which is nylon, not wire. It sags when a cat tries to put weight on it, so they cannot climb it.
I thought my cat Mini (8 years) would hate it is she had always been an indoor/outdoor cat and previously roamed through neighbours' gardens. She LOVES it, because no other cats can get into the garden. Admittedly my garden is large (30m long, 10m wide) so I have effectively doubled the territory my 4 cats have to share. You can tell they see it as home territory now because all the cat trails have gone - they go everywhere rather than patroling. I would see how the 14 years old felt about it before worrying about finding her a way out.