I used to have major problems with local cats. The best solution is to get your neighbours, the ones with the cats, to sell up and go away. That works a treat.
Most suggestions I tried had limited success. Ultrasonic ones were reasonable but need to be mains powered since batteries run out and the first you realise is when your lawn is covered with crap again.
You can get auto water sprays when they are near but it is of limited use at the front as no one has an exterior tap there.
Then there are the plants they are supposed not to like, but which need replanting every year, or the chemicals or lion crap that is supposed to scare them off too. Or one thing that did seem to have an affect was camphor.
Your problem is though that it isn't just soiling you wish to be rid of, but to change the nature of the beast to not chase your wild birds. I think to an extent you just have to lat nature take care of that one and the foolish birds suffer so the next generation is smarter.