Jab at their shoulder/arm, back away. You are not doing any damage like that; but, if they want to win the round, they'll be forced to open up and attack you.
Never sparred anyone who used it but wouldn't hitting them anywhere at all work quite well... You won't touch the chin much or body.. So punch their shoulders, arms... Just anywhere. Used to bug me watching people try and headhunt Floyd round after round when they just weren't going to touch his chin
Yes this is a good approach to take. Just start making contact with your punches, don’t even worry about the chin at first. The chest area is often open to punches too. The worst thing to do is just to try to throw straight rights to the chin, like Canelo was trying to do to Mayweather. The guy will roll it and counter you all day. Straight rights will only work if you have a significant height advantage.
A guy is susceptible to the roll if he is close and throws his punches, but a jab from a distance like Thomas Hearns would make a guy with a shoulder roll ineffective. Jab jab jab and then throw in the right when Floyd (for example) is thinking about the jab.
Come up the middle. Use feints and Jab and lead right hands to the head and chest. Once they start dealing with this you start doubling up with the left hooks to the body and head and throws those over hand rights. Eventually this stuff will start getting through.
I think there are two effective ways. One, a good left hook or uppercut (against a right-hander). Two, throwing the shot from up high and coming down on the head, as GGG has done against several opponents. Rolls and Rubio come to mind where he used this to take them out.
Punch down, not up. The shoulder is protecting their chin not their temple or eyes. You probably need to be taller or love overhand rights, or have weird angles like golovkin where he raises his fist above head to punch downwards. Other than that, seems like workrate would have been it, saw that with Castillo and maidana. Porter would have been interesting.