Looking for large container (30"X30") soil recipes.

I lost large perrenial plants in 4 big glazed pottery pots last winter, we had unusually prolonged freezes here in Austin, Tx. The plant that survived had to be taken out as all the pots were water logged and smelled sour. I'm starting fresh and plan to put in yuccas and agaves and need a soil recipe that will drain and not compact. I hear of expanded shale, etc. but have never used it or pumice, grit, or coarse builders sand. I want to know what has been tried succesfully along with compost. I've also heard you should fill 1/3 of the lower volume with rocks. Palmbob, anyone?

Skip the "drainage layer" of rocks. http://davesgarden.com/community/forums/t/1073399/

The Washington Post "Local Living" section just had an article on the subject of growing succulents in containers (May 20, 2010--"No Water; No Sweat"). You can find the article on the net, but you need to register (free) to download the entire thing. Anyway, at the end of the article here's what they say about soil:
"You will need to make a special growing mix for planting succulents in containers. The blend, basically, is one part of a compost-based soil mixed with one-part gravel such as pea gravel or granite chips. Don't use sand, which can become too compact and be continuously moist. This would lead to root-rot. A one-inch layer of pea gravel or other pebbles will give the container garden a finished look and keep the crowns of the plants particularly well drained."
I agree with Puddle Pirate about skipping the bottom drainage layer of rocks.

An excellent and extremely durable soil that holds good amounts of water, yet no perched water. It will never compact, has superb air porosity, even at container capacity, and will remain perfectly serviceable long beyond the point where plants should have been repotted:

Al