How can I best create a motorcycle tie-down point on or through my cedar fence?
I like the buried chain idea. In fact, you don't even need to use cinder blocks. They make 'earth screws' which are large auger-looking thing that you literally screw into the earth. Typically used as playset tie-downs or party-tent tie downs. 



Alternatively, maybe attach a bar to one of the fence posts. I'm thinking one of the stainless hand-bars you'd normally mount in a shower. It's one piece, shouldn't rust, and would look OK.