They are commercial products that even with the wedges driven a tight as I can get them slip upon hard usage. I assume the are hung properly. Pinning is all I can think of.
Hello Doc, pinning is only of use to stop a loose head from taking the head off whoever is in front of you (which is why I pin). Try adding a small cross wedge as well as the large wedge, and soak the head of the axe in raw linseed oil for a few days/week.
I also cheat a bit and add some Gorilla glue to the haft and wedges when I put them together.