The best defense is a good offense.
Be very, very careful in housing and gear assembly. When you get "on location", assemble your entire rig, including flashes, sync chords, etc., only after completely disassembling anything with an easily serviceable o-ring (sycn chords, housing gaskets, port gaskets, etc.). Do not over-apply your silicone greases, and be sure to use the one rated for your products.
I would suggest removing the o-rings entirely, then cleaning the o-ring, and both seating grooves of the part. Do this with good quality cotton swabs. Re-apply the silicone grease to the o-ring (main key is not too much. and "pull" o-ring between thumb and forefinger to uniformly coat), and inspect the housing/part grooves in very good light - with a magnifier. Carefully assemble the housing/cords/whatever, and make sure you don't "pinch" the o-rings in any way (if you do, you may have cut them, and they need to be replaced. Always a good idea to have a spare one - especially on the large housings, as they're only around $5- $6). Check to make sure no hairs, etc. are in the grooves when you do the final close, too. Q-tips work great for cleaning the grooves out, too (don't buy cheap ones, as they can leave fibers in the groove). I flooded a $3000 video camera once, due to an eyelash on the o-ring. Everything worked fine until around 80 feet, then the floodgates opened. Amazing how well my dive buddy could understanding my cussing underwater.....
DAN actually sells flood insurance, too. I forget how much it is (I have it, as my total rig cost is around 9k, and if you flood it, you'll ruin the camera and lens).
The old axiom of it's not if you'll flood one, but when holds true. After flooding 3 housings (1 was faulty housing...but I got a new housing, but no new camera in the deal), you'll take a back-up unit. I have not flooded a housing in over 5 years, but I have developed a strict pre-trip protocol, as well as strict post-dive one, too (very, very important to soak you housing in fresh water for at least 1/2 hour after your dive day is done. Don't open or disassemble until after this soak is done, as salt crystals form on the gaskets/glands, and will cause abrasion to these items, if the buttons are pushed, etc.).