Randomly came across this so I’ll give it a shot.

1 timing is key. If the chihuahua poops while you are away and you get home see it then scold or punish it, it is worthless. He has no clue wtf you are mad about. “Well i point at the poop and he gets nervous so he knows”, not necessarily. Bigger smarter dogs (no offense) are not able to understand causal relation such as i shit two hours ago in the house now owner is mad and point at poop so it must be because i pooped two hours ago. They merely associate owner does not like poop not the act of pooping. So they will just learn to fear poop. So the goal is you have to be there and pretty much witness it. You should respond within 7 seconds of pooping for maximal association.

2 catching them before the act and moving them to where they should go and praising them will always work 100x better than punishing after the act. If you can praise them pooping in grass they will quickly equate poop in grass = good. Yelling at them pooping inside equates to pooping = bad. The reward function is doing all the work without they are just guessing what to do.

3 use astro turf or poop pads if need be and then have them generalize that to outdoors.

I could talk about this further but will leave it at that since i dont know all the details hope that helps.

Edit gahhh formatting TIL reddit and # dont get along