A few things can cause slippage that require no physical mods to fix.
1) don't over inflate the pad. A well inflated pad slips easier. Inflate, lay on it, let out air until it's comfy.
2) make sure your tent floor is level. The slightest incline and you'll eventually roll off, especially if the pad is hard.
3) box yourself in...you can lay jackets, packs, etc. on both sides of you which will help keep you centered.

I cured this by going to a Ridgerest foam pad. In my hammock it doesn't slip at all and I'm warm down to 18 deg. with it and no underquilt. My inflatables take up closet space and have become loaners these days.