My experience is similar to Spark’s. I generally don’t get marks, though it has happened. Full on ball busting - kicking/kneeing can lead to bruising especially harder sessions. I also have gotten cuts from kicks. I also find “misses” happen and the inner thigh can bruise easily.

Squeezing, crushers, light busting probably less likely to mark. Fwiw, I’ve found even light busting with taps done over and over in the same spot can be excruciating so definitely ways to deliver lots of pain there without marks. Electrical is probably another good choice.

Have fun!