I have had good luck with buried wood. I put buried wood throughout my vegetable garden, excavating down about 18 inches and filling with logs and brush. First 500 square feet with pick and shovel, second 500 square feet my husband took pity on me and rented an excavator. Last summer the buried wood areas survived when parts that were just mulched died during the heat and drought. Thicker piles of wood would probably hold even more water, but I think in a dry climate they should be at least partially sunken into the ground.
If you have more wood than you want to bury, if you pile it in a dense low pile it is not considered a fire hazard (according to Bill Mollison). These kind of brush piles decompose pretty quickly. If you put the brush in low windrows on contour, it can help stop erosion. Throw some seeds in there and presto, hugelkultur!