Something other than grass, like a bunch of shrubs. With thorns. Roses are good. Aromaatic might deter dogs, too. People in my neighborhood sometimes have "please clean up after your dog" signs. Pee is generally considered okay, but leaving dog poop on your neighbor's lawn not okay.

other than some sort of landscaping rock or covering the whole area with shrubs, i don't know much you could do. dogs will even do their business in rock so even that option may not work.

have you tried talking to the owners? of course, they probably don't give a rat's patootie but i'd at least let them know how unhappy you are about this. is there a leash law where you live? if so and these dogs are running loose, i'd consider calling animal control.

it's people like this who give us good dog owners a very bad name and it ticks me off to no end! i have 2 great danes and i would be absolutely mortified if they went around peeing and pooping in other people's yards!!!

I'm sorry about your inconsiderate neighbor. I have a dog and love dogs, but no one likes dog poop and it is unbelievably bad manners to not pick up after your dog. Dogs can and will poop on nearly any surface, especially grass, gravel, bark, etc. And unfortunately once a dog starts using a specific area, it's common that they will continue to use that area and that other dogs might do the same. I've experienced this with a bad neighbor before and it only ended after the neighbor moved.

What size are the dogs using your property as a toilet? A smaller dog might be easier to deter than a giant breed. What kind of resrictions (besides fencing) does the city put on the property? Can you plant anything you like?

If the city allows, you could border the entire section with unfriendly shrubs that a dog would be less likely to step over or use. I'm thinking something like yucca, which would be unpleasant to step over or squat over.

Some ideas using Carissa Holly & Gold Sword Yucca:

Add a stepping stone path so there is a clean place for your family to walk. Poop on the pavers would be noticeable and easily avoided.