heckythump - i know what you mean about the fish one! banned from our house too, our boy didn't like it either.
sorry to hear about your dog's problems, poor thing. i think slippery elm is definitly worth a try - i found out about it when googling after ours was diagnosed with colitis. it works by soothing and coating the digestive tract, it is safe for both dogs and humans.
buy the powder, not the capsules. if you get the capsules they cost much more and you have to break them open anyway! i mix a teaspoon or so with a good splash of boiling water and mix it through his food, or sometimes through natural yogurt. i do this once a day but if his tummy is dodgy then i will give it twice.
i had a google to find out the dose - there are different doses out there but this works for our dog.
the only thing you need to be careful about is giving the meds, the advice i found is not to give it at the same time as slippery elm as it can affect the absorption of medicines.
hopefully you will find the slippery elm helps him. i would have a good old google and get as much info as you can, start him on the slippery elm and if it appears to help then maybe take the info to your vet and speak to him before reducing any meds. our vet knows we use slippery elm, it is on his notes, but had never heard of it himself.
as to dh - yes, he finds it good. he tends to take it if he knows he will be eating/drinking something that can set his ibs off. i know someone else who uses it more regularly for ibs and finds it really helps too.
hope this helps. let me know how you get on with the slippery elm!