Yeaaaaaaaa they are like the iceberg that sunk the titanic. It looks like large but overcomeable size rock for the backhoe on my tractor but I would end up excavating a 6ft perimeter and pulling basically a car out of the ground. Makes for good paintball shelter in the woods!
I think my concern is that while rock like that is common, and I really won't know until I start digging so sounds like I need to just get cracking and determine what's going to work best for each post. Uniformity is overrated anyway!!