imho, clay is the only way to go (especially from an electric and maintianance viewpoint).
ideally a reasonable thickness of clay needs to be layed down to prevent cracking/break up etc.
over the years, the last 2 loads of dirt have been the best.. the dark clays cracked up too much and were a pain to maintain.
the latest one was a bit thin, that's why its down to alot of rocks and sand coming up through it now... but when it was 1st put in it was smooth and rock free for quite a long time.
i spose for all the rain there's been, with very little maintainance that thin layer of clay has done pretty well.
when the new track goes in, something to think about might be the start up of an atleast montly working bee (especially if 1/8th scale are going to start running there?).
perhaps something like bonus points for the standings or a reduced race fee for those who attend working bees might be a way to encourage more to help. recently all the track work has fallen on the shoulders of only a couple of people.
the other thing that would help maintainance alot, would be (if possible) a fence along the carpark side of the area. just to not allow 100% free acces by bikes to the track and hopefully give the impression its fenced off for a reason.
back when there was alot of rain we were forever spending hours on the track just patching up the ruts from the bikes.
hope to be back out there soon.