I believe you can make a Cobra reasonably safe for the driver.
All you need is a full roll cage with side impact bars, race seat with head restraint (side helmet wings also) HANS device, top of the line helmet, fire rated race suit, wrist (arm) restraints, fire system, fuel cell, and ONLY drive on a race track where people are not on their cell phone, drinking or eating, and everyone is paying attention to driving.
Other than that all you can do is drive as if you are invisible, and PAD that roll bar with the best high density (race approved) roll bar padding if you have one! Most of us do have them I know.
As for making one strong to protect you in a roll on a race track, it must be tied to a very strong part of the frame, must be braced, must be above the top of your helmet... in other words, it must meet strict race sanctioning bodies rules for roll bars. Otherwise it is really just for looks. The pictures posted here of various Cobras that have rolled, just imagine what the drivers head would look like if he was not wearing a helmet when he rolled over.
BTW if you have not as yet watched the "Texting while driving" PSA video made in England,
WATCH IT! The recreation of an accident is very, very powerful. Ask yourself "how would I do if she had hit me in my car"? As you watch the violence of how the passengers are thrown around imagine not having air bags? What would my roll bar do to my head?
Don't fool yourself by thinking it could never happen to you...
Roll bars look great but driving is deadly, the most dangerous thing most of us will ever do. The danger usually comes from other people on the road who do not recognize that fact, and who don't enjoy driving, so they do as little of it as possible when behind the wheel of their car....