Rat poison comes to mind, but then you like animals so maybe not
What to do? If you do not have a fence, and they do not want to pick up after their little beastie - you may just have to grin a bear it and pick up the calling cards.
Retaliation such as leaving presents for your neighbors make bad neighbors worse.
For about $30.00 you can get plastic fencing at a home store, these are usually in rolls and come in green, brown and bright orange. They are used to temporarily fence off an area in construction sites, say marking off an area where the bull dozer is to not go.
You can get plastic covered steel vegetable poles 6 feet in length, these have a pointed end and are about 1/2 inch in diameter. They easily penetrate the soil. Set one every 8 feet and tie the plastic fence up.
Unless the dog is just contrary by nature, he will find someplace else to do his business.
You might try talking to your neighbors again, but if they didn't listen the first time, I doubt they will again. There are a good many people in the world who do not listen and no amount of talking works.
The plastic fence is a short term solution. You will need to think long term as well.
Chain link fencing is sturdy and lasts for years needed nearly zero up keep - but it looks like prison fencing and you can see through it.
Another option is wooden fences. These require staining or painting every two years to get the most life out of them. If you do go wooden, you tell the person who builds it that you want each post to be 24 inches deep, sitting on top of a doby (a small brick used to hold up reinforcing rods in concrete pours) and you want the whole hole filled to the top with concrete.
You may have to stand over them while they set the posts to make certain this is done. Many fence people tend to dig a hole, set in the post, half fill it with dirt, then top it off with concrete. Wood will rot in contact with soil. The method above extends the life of the posts - which is usually what goes first on a wooden fence.
Cheers
David
