wipeout,
I have a few suggestions on this. However, I do not agree that the socks are useless. The socks prevent rubbing along the length of the shaft.
Here are my suggestions, First…make sure your clean. I usually use the Power Jelqer just prior to putting on the PM. Then I take a shower and make sure I am very clean of all oils. With my penis in the swollen state after using the Power Jelqer (PJ), the head is enlarged and assists in the prevention of slipping.
If you are not using the PJ, you might try this. Wash yourself and make it squeaky clean. Then get a slight erection. Make sure that when you put on the PM that there is plenty of blood stored in your glans so that it will hold better. I sometimes, due to the slippage, will use my PC muscles to attempt to engorge my head just as I tighten down the strap to my perferred last notch.
Here is another trick that I have worked through. The strap will slip sometimes too…notch by notch. I use cable tie velcro straps to hold the strap steady. I also believe the velcro cable ties increase the life of the strap. The straps will loose thier elasticity.
Hope this help,
Manzwa