Funny your response. I was just about to get on and pose that very idea. It seems that what I am talking about doing is NFT as I now understand it. Additionally I have read some posts from Oldmac, who will hopefully chime in here soon enough, that talks about this very idea when responding to someone elses concept. His idea turned out to be the very thing I am trying to do. Apparently just about everyone who winds up buying an ultrasonic fogger seems to take the same path of discovery and wind up at the same conclusions that I am now. Hopefully I will have a proven system soon enough to be able to post the results. There are no good fog write ups for this kind of fogger. At any rate, my idea was this:

Line the bottom of the fence post with one single layer of hydroton. It just so happens that I have several bags already. Then locate and install either a single spray head or a fountain at one end to supply the supplemental watering. The flow of water should be no higher then about half way up the layer of hydroton. As you mentioned earlier the water would flow and mix around, but it would be a gentle enough flow to not splash my fog roots. Also it occurs to me that since I will be using air stones and low water levels that I could probably leave the water running 24/7 which would keep things simple in terms of timers and pump wear. I will also be using 24/7 fog which again is a benefit in terms of timers and pumps. I am fully aware from others and my own experiences that using dry fog 24/7 is about the most successful way to use this kind of fog without much fear of root rot. So given the fog environment and assuming I install a layer of hydroton, I eventually expect to find the roots firmly rooted to the bottom and actually begin to grow fog roots back upwards. My wife seems to think that roots are incapable of growing upwards so I don't know about my last statement. None the less I think a layer of hydroton would be better then a bare ass bottom like you say. If nothing else it would even out the water flow.