Moved MPSIMS --> IMHO.
This does sound odd. I’ve been around dogs all my life and I don’t think I’ve ever seen one the would prefer a mat over grass or dirt. That would be like taking a dump on the sidewalk.
My dog was doing this. Possibly because my neighbours dogs are tied in their yard and she wanted to … shit on their doorstep. :smack: Also it’s nice and dry over there - she doesn’t like to get her paws wet.
The thing is really not why they’re doing it but how to get them to stop. Since my dog was the one with the issue I dealt with it, by grabbing her and putting her on a lead for a few hours tied inside our house every time she made a move to go over there. Pretty soon she stopped - or so I think, I must double check with my very polite neighbour.
Well, if the grass is tall and the dog is low . . . maybe it tickles.
Why not ask your friendly neighbour to help?
I was just about to ask this. OP says they are friendly with neighbor, so why not a quick “I think your dog has been using my door mat. I want to make sure it’s not going to happen when I replace it”
I think the first thing you have to do is discover who/what is pooping on your mat. Accusing your neighbor/neighbor’s dog could cause hard feelings, regardless, but blaming the wrong he/she/it could be a wee bit embareassing. just sayin’
Again, my guess is that it was trained to use a pee pad in its home, so it associates mats in general with that purpose.
Thank you for your replies. My neighbor (owner of the chihuahua) and I share the same courtyard. There is only one dog, the chihuahua. It is not a problem for my neighbor, only me. I was hoping I could discuss this with the chihuahua. And teach her that this is unacceptable behavior. Just curious why she prefers my doormat.
All dogs understand shoe. 
Have you ever seen that “Texts From My Dog” page? I’m thinking something like this:
I WAS REMEMBERING MY CHILDHOOD TODAY
Oh, that’s very sweet.
YEAH YOU USED TO LET ME POOP ON A MAT INSIDE
Yes and…
I FOUND ONE JUST LIKE IT TODAY
Oh no
IN FRONT OF NEIGHBORS DOOR. FELT LIKE A KID AGAIN
^^ heheh…
My (clueless) neighbor’s cat used to poop right outside my back door on the mat. Also right outside my car door on a mat there. We took away the mats and the cat died anyway, so havent had the problem anymore, but anyway… I mentioned the fact to my neighbor that I actually witnessed her cat pooping on my door mat.
Her reply: “Oh yehhh :rolleyes:… He does that in the house too: he poops outside the litter box but not in it.” WTF?? Why do ppl put up with pets like that?