I often carry bottles in checked-in luggage. I lock my checked-in luggage except on the rare occasions I go to the US. Perhaps I've been lucky, but in years of travelling I've yet to lose checked-in luggage. (Sometimes its been damaged or delayed, but never lost contents.) I've taken the view that the risk of breaking a bottle as you carry it around is greater than if its safely stowed.
I always carry plenty of bubblewrap and wrap bottles in that. I'll roll the bottle up in several layers and then put in a plastic bag, or use tape to stop it unwrapping. If they can't knock against each other or another hard surface, they'll unlikely to break. With enough layers, they can even be dropped from quite a height without breaking. If you're carrying anything else in your baggage of value that would be absolutely destroyed if wine got to it, then I'd seal them in a bag just in case.
Bubblewrap does add bulk though... when I pack bottles they pretty much double in size when I've finished with them.