Here is a link to the PetCo locations in Louisinana:
LA PetCo locations
And here is a link to the PetsMarts in LA:
LA PetsMart Locations
Both locations carry better foods than the Purina brand. I feed four dogs the Sensible Choice Natural Blend Holistic Formula by Royal Canin which I get at PetCo and all dogs have great coats and not alot of poop.
If you've taken the dog to the vet to rule out a medical reason for loose stools, I would restrict food for 12-24 hours to give the dogs stomach a chance to settle, and then begin to feed only a small amount of food for a day or two and see if that helps alleviate the problem. You can also feed canned pumpkin (NOT the pie filling with all the spices!!!!!) - that will help firm things up.
Good luck!