Looking for "Chain-slap" solution...

On the heavily rooted trails I ride on ( Quiet Waters, Oleta, etc) the chain
on my Trek Liquid 25 starts flopping around like crazy when I hit race pace
speeds through the rough sections. This is not an issue on trails in North
Florida like Croom or Santos ( meaning it would be a non-issue in N Carolina
and other real mountain biking locations). But for my weekly rides, I need
to find a way to reduce this flopping around. Sometimes the chain will shift
itself into the granny gear, when I "need" to stay in the middle ring. and
other times, when really hammering a rough section, the shifting on the rear
derailer is badly compromised by the flailing chain.

The only possible solution I can think of is removing the Big ring from the
equation, and taking out several links--shortening the chain, in the hope
that this will mean less travel potential for the chain....I'd rather have a
better solution, and am hoping someone has one...

Dan V