Giardia is a very persistent bug and may take many courses of treatment, and different course of treatment to cure.
Other possibilities include food allergy, pancreatic insufficiency, and other as yet identified GI parasites.
I would request another course of Metronidazole or Panacur and place your dog on regular kibble during the treatment. If diarrhea continues on the kibble, request a hypoallergenic prescription diet from your vet as a therapeutic trial.
I see that happen at work where I'll treat an animal for various parasites only to have to repeat the treatment again. Did you have a follow-up fecal done after the meds? Did the doctor recommend using any probiotics to get the gut flora back to normal? Perhaps the coccidia is gone now but your dog has developed a sensitivity to the kibble. The rice diet might make him feel better until the intestines heal up but I don't know if he can stay on it indefinitely, whether it provides all the nutrition he needs in the long run. Sounds like he'll need a visit to the vet again.
We had a follow-up fecal after the first round of meds. That one tested positive only for coccidia. We haven't gotten a fecal exam since the second round of meds ended.
We have been using acidophilus while on the meds to get the flora level back up.
I called the vet today and they recommened another round of metro and put him back on the rice diet, but to mix 1/2 kibble.
In between treatments the vet had thought he may be sensitive to the kind of kibble we were feeding him, Purina One lamb and rice. We switched over to Purina One chicken and rice which we were told is easier for dogs to digest, but he still had the diarrhea.
Is there a brand of kibble out there that may be better if he does have a sensitivity?