In general, it's easier for me to trim with clippers rather than shave. I always catch my underarms and back with the clippers when I cut the hair on my head. You can shave your butt crack, crotch, and balls with a safety razor in the shower. Use lots of soap and give it a go. I prop one of my legs up against the shower wall and shave the one side of the crack and then lift the other leg and do the other side. After you've done it a few times, you can do it by feel. Love having a hairless crack and crotch. Hair in the crotch sucks if you're into cycling.