Rubber bands über alles (bottle launching solution)
In another thread, I posted my rubber band solution for tucking CO2, tire irons, and a tube under my saddle. Recently, after a few fights with launched bottles (and it's always the FULL ones you lose, of course), I had one of those "doh!" moments and came up with another rubber band solution, which I illustrate below.
The disadvantage of this solution is that you have to stop to get the bottles out and re-mount the one you exchange in. There is another way that i've done it, which is a little less secure, in which you tie the other end of the rubber band to the other side of the cage instead of wrapping it around the bottle.
It's probably not "cool" to use rubber bands on a full carbon frame, but cheap solutions to some things mean you can afford a few other things. 
William
Comments
My last race was kinda interesting - the bike route went through the New Forest (here in England) which is national park - loads of cattle-grids to cross - never seen so many bottles strewn all over the place! It was tough negotiating the debris!
I always take the back thingy off for races, but you gotta have it for those longer rides out by yourself!
On some Ironman coverage I saw Tereza Macel with something like this to hold her water bottles in. She had the elastics near the top of the bottle(the part you drink from) and reached around on the fly to do/undo the elastic. If you did it that way you probably would not have to stop.
William,
I was having lots of problems launching bottles with similar cages on a rear mount - bottles would eject straight up and out with moderate bumps. FWIW I stumbled across some specialized plastic cages and I figured they could not hurt. See http://www.safetycycle.com/speciali...white.html These are probably the best cages I've had, as they are easy to get bottles in and out of and have not launched one bottle yet on any road, and I ride on some tough roads. Worth a look and might require less attention than the rubber bands.
Dominic
Thought more about what Wayne suggested, and I'm pretty sure I can put it up so the elastic is removable on the fly without flying off...and empty bottles are not a problem (at least for me). When I'm using one of these systems, it's for my 3rd and 4th bottles...so I'm exchanging them with empties from the bars and down tube, not using them repeatedly.
I'll post a pic on how my DH does the rubber bands. He's been doing it for years, but it's such an EN code violation, I did not dare even whisper about it.
All I can say from riding with him, it is way better than having to go back and pick up the launched bottles. He loops the rubber bands simply, and takes bottles in and out on the fly.
I've experienced the same success with Gorilla cages. Even when riding Stagecoach Road, and over the sets of railroad tracks coming out of Cross Plains.
My experience:
Therefore, my new solution that works 100% of the time and is even cheaper then rubber bands. Bottles go in cycling jersey pockets... all problems solved and it cost $0.
If I am riding really long and there are no stops, I go two bottles in the jersey pockets, one on frame and one on the aerobars.
2nd on the Gorilla cages. DO NOT LAUNCH!!