Neighbor unhappy about the feral colony in my yard
We have a colony of 9 feral cats that we've been feeding and providing shelter for for a couple of years. Our across-the-street neighbor came over tonight and complained that the cats are coming into her yard and using the space under her porch and her flower beds as litter boxes. I can understand her frustration and she made it clear that she doesn't like animals in the first place so I know it's doubly annoying to her.
My dilemma is what to do with the cats. I can't touch them, so there's no way I can take them inside and with our two existing inside cats that's not feasible anyway. I don't want them to be picked up by animal control and be euthanized. I would like to know of any way that I could keep them in my yard or keep them out of her yard. I looked at the CatStop Ultrasonic Cat Deterrent but have found mixed reviews and I don't even know if she'd allow me to put one in her yard to see if would keep them out of it.
At this point I'm very open to any suggestions the kind people here might have. We have the numbers to the few organizations in our area that might be able to help but I'd like to know of any other options that might be open to us.
Thanks in advance for any advice you can give.