My father has had toenail fungus for decades. He's tried various home remedies and over-the-counter medicines, but nothing has helped. He could take the anti-fungal prescriptions, but, as has been mentioned, they are very hard on your liver. This risk, for what amounts to what is really just a cosmetic gain, is not worth it to him. He is otherwise healthy, and the fungus just makes his toenails looks bad; it is not painful, and is clearly not a sign of other problems given that he has the fungus for 30 years without any other issues.
Maybe your husband just needs to learn to live with it.