My guy tries to mark in the vet's office. He hikes a leg in the same spots where I assume a hundred other dogs have done the same. I just watch him like a hawk when we go to the dog doc's. The last time there, he only made one half-hearted attempt to mark.
I have had a problem with the vets office as well. My male always shows a good deal of attention to a spot before he marks. Now I no longer allow needless sniffing indoors no matter where we are. I travel with my dogs often, and I don't want to worry about bringing Nature's Miracle everytime we stay in a hotel.
Dusk has gotten much better about it. Its now very rare for him to sniff indoors with that deep look of concentration. And I'm sure you know that "look." But I'm very strict on what he is allowed to mark and how often. I refuse to stop every ten seconds on a walk just because this tree smells particularly good.
Nope never had a problem. he goes to pet stores 2 or 3 times a week. never had a issue there. and I would kill him if he started marking in other peoples houses, since I take him so many places with me lol