And so a new phase begins

Sorry to learn of the Cancer progression your husband has experienced despite treatment. Sometimes cancer cells that are too small in number to seen on scans subsequently clump together to form Metastases. If there there are only a very few spots and dependant where they are, they can sometimes be individually treated with radiation to at least buy time. However, if this is not possible generally because they have become more numerous/widespread the only answer is for systemic treatment of one sort or another. It is a long shot but maybe worth asking whether spots of cancer could be treated individually in your husband's case.

Over the years men have tried many non medical things to counteract the effects of cancer but other than trying to keep as fit and well exercised and having a healthy diet (as would also benefit a man without PCa), I haven't seen proven by clinical trials any one thing that would make a great difference. It is important that a man is not deficient in vitamins and where so these are given. Some drugs can cause deficiency but sensible to check with Urologist as some supplements can work against prescribed drugs/treatment.