Next door but one neighbour's cats kept sh*tting on my garden and ripping the bin bags. ( few years ago when bins were inside mesh cage.
Caught the ****** and picked the turd up with a shovel, took it round to their house and knocked the door.
When she opened the door i said this is yours and tipped it onto her floor, some rowing ensured and she told me i need to put orange peels around the bin.
I said you need to frigging feed them, they always on the scrounge.
Anyway, tell your local council if you know the owners address, name. They will/should send them a letter and possible action.
If you have cctv show them it.
Or shovel it up when they gone and post it through their letterbox.
Responsible owners wouldn't let this happen.