rlong

I'm on my 2nd frame due to rear triangle miss alignment and resulting in the chain dropping off the granny gear when I down shift. This continues to happen with my new frame. No real success at preventing this by derailer adjustment (Shimano 105 triple), but it does happen less frequently if the derailer is just barely rubbing chain in my lowest gears (30/28). It will drop off at least once every ride and the carbon shell is really taking a beating (it won't last long at this rate). No way to put a chain keeper on that I can see, so here's my question. Will another front derailer like a deore work better than the 105 and prevent this?
No one has checked the chain line on the new frame yet, as I havn't complained, but I can't believe I could get a second misaligned frame!!