How can we make sure engineers are responsible?
by making the engineer fix all problems he created through his work - pay for all damages following from his work
What do we do about the ones that aren't?
blacklist them :D in reality there is not much we can do except make it known that they are not responsible engineers - however after the first mess-up that cannot be fixed by them (physically or monetary or indemnity) they'll soon end up in jail anyway ;)
Do we have to wait for something bad to happen to take action?
afraid so - you can't make an engineer responsible before he's actually done something
I understand the point you're driving at: sort of a society based vouching through licensing, titles, mandatory training, etc. ... sounds like a good idea on the surface but underneath it only replaces self-responsibility with society-responsibility ... plus those licenses, titles, trainings have been failing badly in recent years - same as our mandatory school system, which once was put in place to give everyone a chance to learn (like training to be allowed to call yourself an engineer) however have been perverted to 'everybody learns nothing as that is the lowest common denominator' ... if you don't have the individual will and ability to learn and train and take responsibility for your actions, then all this mandatory schooling, training, licensing is just pushing that responsibility on to others ...