How to kill foot fungi permanently?

Oral Lamasil: Or topical anti-fungal creams. The hard part is preventing re-infection.

Cut off feet: Joking! but seriously, there is no truly permanent method. The best results I have seen are with taking prescription antifungal medications for several months. These medications can have toxic effects on the liver, so it is important to do this under the care of a physician. It is not unusual for the fungus to come back eventually. Other treatments are available but are less effective.

Very difficult. : It is important to differentiate between toenail fungus and skin fungus. The latter being easier to treat. Fungi are oppurtunistic and look for any reason to come back to you. Afterall, why not? Yu offers them "free rent", a place to live. Antifungal medication is a start. Even after the fungus may be eradicated, i believe maintenance therapy is required to keep the fungus away.

Can kill but: Fungus can be reinfected by fungus. No "permanent cure".

Prevent re-infection: The best way to get rid of foot fungus permanently is to prevent re-infection. Athlete's foot fungus can live in your shoes, on surfaces, in the tub or shower and re-infect your skin. Use the medication your doctor has prescribed and make sure you wear clean socks. Clean any surfaces on which you have walked barefoot. Use a recommended anti fungal shoe spray every day after taking off your shoes.