go faster...hehe!

sorry couldn't resist

stay out of the granny on these....make sure you have enough speed to get you to the top (which you said you do)...have your strongest leg's pedal in the 1 or 2 o'clock position...when your pedal has cleared the top pedal as your pedal is being pushed down you & your bike will be moving forward (together hopefully) so the log will be behind you by the time the pedal is low enough to hit...

this takes alot of practice and hits (the scratches on my pedals say it all...but then again i was learning this on a rocky trail as well)....sometimes a little bit of back-pedaling is required to get your pedal in the right position...and once you have it down with one foot switch and work on putting the other foot forward so no matter what eventually you will be able to power over any log...this really helps on uphill ledges/steps when you are going so slow that when you back-pedal you risk actually going back-wards...