How to get rid of athlete's foot forever?

No guarantee: There are things you can do to make it less likely to recur, like keeping your feet dry as much as possible, letting shoes dry out for at least a day before wearing them again, use an antifungal powder and/or cream, and using an antiperspirant, like prescription drysol, to reduce sweating.

Impractical: Fungi causing athlete's are ubiquitous and it is possible to get re-infected after eliminating the infection with medication. You may need to repeat treatment and keep your environment as free of fungi as possible.