Whilst I wish this wan't the case, I've had to become a bit of an expert in equine wet poos as my childhood ponies have hit their thirties. Your neddie's probs are no doubt not related to being as old as mine, but here's the benefit of what I've discovered - hope it helps!
Slippery elm - it sort of lubricates the intestines to reduce inflammation - this has been the BEST product I've found and not too expensive. I get mine from Hilton Herbs;
British horse feeds Fibrebeet and Dodson and Horrells Fiberygy have been godsends;
Global Herbs do something called Diareeze - not very imaginatively named and smells like curry powder but seems to do the trick - I think it's got psyllium husk in it which sort of cleans out the system;
Haylage, any oils (including linseed) and too much grass (especially in spring) go through mine like a ferrari;
I would never be so brave as to try sugarbeet - I think that would have quite spectacular results;
Bailey's do a supplement called something like destiveaid which is a probiotic and prebiotic and not ridiculously expensive.
I also got mine worm counted and teeth checked, just to make sure that wasn't the cause.
Ooh, and if you have the poo down the legs problem, a good spraying with showsheen helps stop it sticking. Nice.
Good luck!