The plants will not be burned by the hot pepper flakes which should discourage thedog from stopping there.

I would be almost certain the dog lives next door or very close by. Once you find out which yard the poo belongs in, (where the dog lives,) return it. Knock on the door, smile, hey new neighbor, how ya doin, whatever. And, btw, I'm returning something your dog left in my yard. Not upset, not confrontational, but letting them know you know their dog is crapping in your yard and you won't be OK with that.

Thanks for the info and the suggestion :)