Update: One the elements of the treadmill belt that attracted me--toughness-- is also a problem. Because it does not stretch, when the shoe flexes the glue on the toe is pulling the glue on the heel. Walking is fine, but I don't think it will hold. My suggestion is to put one patch on the front half and a second on the heel. Or, use a tire or other rubber slab. I continue to experiment.
I have a pair of Keen shoes, nicely broken in after four years of wear, but with soles worn thin. Friends told me that Keen would replace the soles, free, but their website says there is only a one year guarantee. It was off to the cobbler or DIY.
The first material I thought of was a tire tread. Since I was a child I read about making tire tread sandals, and a few sites have instructions on how to use a tire tread to resole a shoe. Most tires are steel-belted, making them tough and rough for my purpose. Some leads have suggested motorcycle tires, wide bicycle tires and I had thought of a wheelbarrow tire (they show up in our dump) but I needed my shoes fixed sooner and did not have time to research or gather these materials.
While at the dump looking for older tires to use, I saw an abandoned treadmill. Having tried to replace the belt on my old treadmill I knew a) they were tough and b) they gripped well enough. With my pocket blade I cut it off and experimented.
Step 1: Materials
Pair of shoes with sole firmly attached to upper, but thin and in need a another layer. Remember, this only covers worn soles; it does not replace the sole entirely.
Tin-snips, cutting blade or other such tool. You will be trimming, so I found the snips quite helpful.
Shoe-goo. This is rubber cement designed for greater wear. I have read of people using bicycle repair glue or rubber cement for such repairs. My tube cost about $5.00, and I used half of it. Do two shoes at once!
Sharpie or other marker. You will trace your shoe before you cut.
Duct Tape. This will hold the tread to the sole while the glue dries.
Cardboard. The Goo is messy, so save yourself some clean-up.
Vaseline. Put it on parts of the sole you don't want the glue to stick to (i.e., the sides).
Treadmill belt. It is woven and layered and tough. I preferred a tire because of the tread, but for everyday-wear the grip of the belt is fine.