Steel fence posts

I would think your soil is the deciding factor for you down there in Alabama. Here in WI we tend to go down 4 feet to try and avoid some of the heaving from the frost in winter.

If it weren't for that I would only go about 2 1/2' because we have heavy clay here and that would be a solid fence at that depth. But in sandy areas you might need it deeper.

Will wind be an issue for your place? Will you be using sight barrier? All thing to consider.

We recommend a minimum of 50% depth vs exposed pipe, thus a 10' fence needs to be driven 5' deep resulting in 15 ft of pipe. For corners and brace posts we use 3" pipe and for line post we use 2-1/2". All horizontal and diagonal pieces are 2" pipe. All joints are welded. Bolt-on connections are an accident waiting to happen.