Keeping Neighbors Pets From Defecating in Yard

Put up an electric fence. ; )

Save your citrus peels (i.e. orange, lemon etc) and either grind them up in your blender/food processor or chop finely with a sharp knife and sprinkle liberally over your garden area. The pets despise this scent and will hunt other places. Just remember to respread when it rains (or you water your garden) to keep the scent fresh. It won't take but a few applications until the pets 'get the message' and will leave your garden alone without further treatments.
I have used this method for my neighbor pets for years, only having to repeat when the neighbors acquire a new pet.