Any tricks to prevent rear-rack bottle launching?

Mountain bike cages seem to hold them better.

Sounds weird, but my Cervelo P2c has no seat-tube bottle mount. Only one downtube mount. So I can't do two bottles in the "A" of the frame, and an aerodrink.

I dumped my X-lab rear rack for the same reason.  I now use a Profile Design rear rack and no ejections yet.

My water bottle configuration is 1 frame mount, 2 rear mount and 1 on the aero bar for drinking.  I have used the aero bar idea for a couple of years now but I just rest it on the bars.  So I’ll remove a bottle from the rear rack after I get going and place it on the aero bars.  I am pretty good at keeping it there and only drop 1 bottle during training.  I don’t use the rear rack for sprints and remove it.  Next week I'll configure bottle a rack on the aero bar so it's more secure and then test it out.    

I've used my rear mounted Profile Design well over a year now and it has never thrown a bottle. I use my aero Profile Design for racing and the rear one for training rides and centuries.

You might give this a try:
http://www.trisports.com/beaker-concepts-h-5c-rear-hydration-system.html

Its the only other rear hydration system I have found for my P2C.  I had the Xlab first, had the same problem with bottle ejects in two consecutive races.  With the beaker concepts, I haven't had any ejects.  Could be coincidence, but it seems to be working better. 

I've launched a ton of bottles from the Profile rear cages and broken 2 sets of them within the last 6 months. Not a fan of Profile.

I do like the duct tape idea. Bottles are smooth. Duct tape is textured. Sounds good.