Get yourself a pair of Birkenstock surgical clogs. They are extremely ugly, but they are the best thing if you are on your feet for extended periods of time. I have worked many 36 hr trauma calls and they were the only thing that did not make my feet hurt at the end of a shift. I tried $150 running shoes from every brand, I also tried a variety of hiking shoes, but the clogs proved to be the best. They are very supportive as well. When you see them you are going to think that there is no way that they are going to be comfortable, but definitely give them a try. They are made out of rubber, so you can get them as wet and as dirty as you want.
Good luck:up