I never had much luck with duck tape. Nor with moleskin, though that depends partly on how old it is. My feet are so oily, most adhesives don't stick well. The tape or moleskin would just slide down and create new blisters in the new location. Fortunately, I don't get blisters much any more, now that I've stopped wearing leather boots. For toe blisters, which I get when roadwalking, I'll use toe bandages - a kind of foam tube you slip over the toes. Otherwise a good athletic tape generally works. I'll do a bandaid and then tape over it heavily. After the second day, there's very little pain, so when the bandages come off, I stop worrying about it.