Sewing a small silnylon patch on your Scrotum Sack is another quick fix if you're worried about taking the duct tape off when you get home. I've had to do this few times. It's best to find a park bench to do it on though, as you don't want to lose the contents of your sack in a bush or long grass.
Generally speaking Scrotum Sacks are not very abrasion resistant. When climbing over a barbed wire fence it is best to carry yours well over your head if you can. However if you do suffer a tear a quick field repair can be done with industrial-duty duct tape.