I have an entranceway between my house and a wall. There's a concrete walk in the center with small patches of dirt on each side. I want to put a wooden gate across with the posts sunk in the dirt. This morning I dug down on the wall (hinge) side and hit the wall's footings 9" down. The above-ground height is 45", so I was hoping to get down 24". I also read two experts' opinions that concrete isn't necessary and can increase the chance of rot. I'm using cedar 4x4s and planning on attaching them to the walls (stucco) with lag bolts. I'm in Southern California, so no frost line. I estimate the gate will weigh 35-40 pounds. My question is: if I pack the post in gravel and bolt it to the wall, will 9" be deep enough to keep the post level?