Many of you have seen this sort of tapegag, popularized on both TieGuyUK, CapturedGuys, and Bondage Jeopardy. It’s called mircofoam tape, and can be easily ordered on Amazon. You can put it directly onto skin, it’s adhesive properties is only a tad more sticky than a post it note (though you may was to be careful with a full beard, of course). And also shows off great definition of the lips, as you can see in the TieGuyUK and Shackler pic. I hightly recommend it!
