I have an inch of sand, and for the big plants you see in my picture i try and put little mounds around them. Also instead of just one loop of lead weight, iv double wrapped it around so it doesnt move even if the sand is dug up around them (damn cory's).
I would show you a pic but my so called clean up crew (shrimp) have managed to turn my nice clean sand into a carpet of tube shaped cr@p! I thought they were supposed to keep the tank clean!
If planting the tank i would have a layer of soil below the sand, and then only a thin layer of sand so the soil doesn't go anerobic and foul the water in the tank. Plants can go alright in sand alone, but better with a soil layer below.