A caution on marbles, I used them one time and was concerned the marbles potentially were going to break the carboy banging around when either carefully going in or taking out. I ended up angling the carboy almost on its side to get them in. You could test the marbles with water in a carboy before committing to the wine to get the same effect. Carboy's have thick glass on the top and bottom but the glass gets very thin 1/8" on the vertical sides.
My concern is heightened since I have broken a wine filled full carboy once by lightly knocking it against another full carboy. Starts with a small leak, then the glass break spider webs out, then boom starts spraying out under pressure, then imagine trying to stop a hole in a dam with your finger but panicking...not good. Managed to tilt the carboy away from the break and pour the contents into a pail saving most of the wine. Just being safe.