Over the years I have used quite a few different methods for keeping bars harder and lasting longer.
One way to keep soap from getting mushy is to use older bars. Natural soap can be used in a couple of weeks at the earliest, but this is also when the water can wear away your bar in a week. Keep your bars in a cool (not hot) place, out of the sun, to continue to cure. Depending on the ingredients, your bar should keep its fresh and aromatic scent for months.
The biggest factor, after cure time, is to keep your bars out of the water, or from sitting in any water. The following is a list of ways that could help:
1. without a soap dish, place your soap on end and keep the wide sides off a damp surface. I did this for years, but I had a non-stop supply of soap;
2. again, if no 'proper' soap dish, fold up a face cloth and place your soap on that. This is the method that I found to actually work the best;
3. ceramic type dishes - they look nice and keep your soap in a bowl-like container, but make sure that water can drain through the bottom of it;
4. wire rack types - yes they work but if your soap is mushy or soft the wires may cut into your bars. A good method to really allow the bottom of bars to air dry;
5. soap dishes with slats - these work well too, depending on the slats. I found that wooden dishes with wide bars did not dry the bars enough between uses;
6. almost any method will work as long as the bars get to dry between uses. I've found that with my family, my children insisted on using the latest toxic body wash and left my soap alone. But with age comes wisdom, and now that my bars are getting used more often in a 24 hour period, these bars are not getting the drying time they need to ensure a longer life. I have since had the kids all pick their favorite natural bar and set up a 'station' for their soap. This has helped all bars dry between uses.
From "how to keep soap from getting mushy" to oils that help make harder bars . . .
All soaps will get mushy, here's info on glycerine-type bars . . .