I went to Hoigaard's to buy Keen's sandals for walking and ended up with Chacos instead. The person there said that the Chaco brand had more support and was the only sandal they had officially recognized by the American Medical Podiatric Association for extensive walking (hiking). Another nice thing is that Chacos are adjustable; I was going to break mine in, but they've been very comfortable since the first time I wore them. If you feel like you might need more support, you could check into Chaco footwear as well as Keen. Both Hoigaard's and Schuler Shoes had both brands, so you can compare what feels best. Other places may have them as well.
http://chacousa.com/ is their website for more information.