[Lopsi]

I have found that when this happens (I also have 2 yorkies), I usually catch it relatively quickly - we don't let messes sit around.

If I get a half-stern voice and ask both of them "WHO DID THIS?!" then the one who did it USUALLY tells on themself - ears back, bulging fearful eyes, looking away, maybe even running to hide under the bed. The other is looking at me like, "Who did what? Will you pet me now?" It's funny how much they actually tell on themself - and although you can't do much to punish at that point, you would at least know which one is doing it and know which to watch.

I know when Pixie starts doing that, if I take her outside a few times and she goes when she's out there, then she'll start shaping up again. Usually, she only does it if it's cold or rainy or something - and then I take her out (force her outside) and she'll go. It saves the messes in the house, but I've learned which is doing it and found the pattern of why.

Sometimes just the asking - and them telling on themself (maybe a few times) and getting scolded is enough for them to realize they can't get away with it.