I know someone who works at a local veterinary clinic where multiple vets and staff carry, including or especially while at work. Very covert, I only know because I've talked guns with a few of the people there but I feel a lot more secure once I get inside the building there from the parking lot.
As has been mentioned here, a lot of controlled substances in the clinic and people on the street know it. The clinic I'm thinking of isn't in a bad area but it's kind of on the edges of a not-so-good area, so it only makes sense. Once or twice in the last year they've basically gone to a clinic lock down when the police were (on at least two or more occasions) searching for an escaped criminal/fugitive within a block or so of the business.