The couple a few doors down from me used to let their two large dogs out for a wander (before bed I assume) at night, I'd usually know when as one of the cats would usually come hurtling through the window).
A few times I looked out and they were on my front lawn doing their business which was just left there. It surprised me with them as they were lovely. I never ended up saying anything (I'm a wuss) direct apart from mentioning my annoyance about stray dogs doing their business on my lawn, hoping they'd get the hint. They've moved now.
The stray ones thing is annoying though, often the same dogs which I assume either escape or are let out to wander, usually too aggressive to be approached and one is a large dog I wouldn't go near anyway. The local dog wardens are pretty useless about them though. I report them as missing dogs but they won't come out after around 5pm unless the dog is contained!