FiNd a public pool and swim laps on non surfing days. I swim a mile daily and I swear it's the reason I have no back issues. I am pretty old, and to take up surfing and not get back issues is pretty good. It's the swimming.
sometimes back probs are a combo of getting old and the use it or lose it aspect of aging muscles.
this approach - a la betty - is imo the best approach to staying young and fit.
well, on top of the back pain, I somehow managed to get a crick in my neck. I went to the beach and was so stoked, I forgot to take an advil (or a leash), but I kinda forgot about my back and neck and was fine. Definitely felt it all again once I got out of the water, but layed down for the rest of the day and it didn't bother me.