Two things come to mind and the first one is not meant to disrespect and that is to learn to remount better. I recognize it may take time and you'll need a more heavy duty seat but remounting is the real solution to this problem.
Remounting is like a hurdler going over a hurdle, your not going up and down, more of sidewise gliding onto the seat.
I'd recommend a Selle Italia and Thomson Seat posts. I hope this helps, and again I don't mean to slight but if your breaking seats your remounting incorrectly.
I did the Cycle-Smart camp and learned to remount much better but I'm still missing some during race situations but I'm still practicing.
I've got very thick skin when it comes to me and CX. I'm not fast, nor am I good at it...I simply love doing it. I have taken a "Techiniques" class or two but find that I get sloppy when the fatigue sets in. I am also built like a linebacker so even gently gliding into the saddle would still stress it out more than the average cyclist. I'm already riding a Thompson post...and I have located a Selle Italia in my collection that will be given the test.
Concur with Neil. Technique is free. That your technique fades when you get tired is normal but it indicates you need more practice. When you're tired you fall back on what you've done the most. In my experience a lot of people learn to do it fast but not right.
How about a MTB saddle? I know some are dual use, but the dainty road ones may be a little slight for your style. I had a Kore Distance Ibeam saddle on my CX bike for some time until one of "my flying remounts" broke the seat post’s rail clamp mechanism. The saddle was awesome, the clamping mechanism - not so much.
Now I use a Selle Italia SMP Strike saddle for road/mtb/CX/commuting (one bike many uses); it's very nice and quite strong, but not for everyone.
Also, head over to your LBS and tell them what you need - I'm sure they have something that should work.