Fence Strength

Hi all, Loving this game.  Only new and jJust a question re fencing to secure your building base area.  I searched high and low and cannot find anything on fence strength and which is suitable so maybe my game is just glitching?  I have used Stem wall thinking it will be stronger.  Will any creatures get through it?  I havent yet seen any come through a main fence Ive built but at the end of the pond where the orb spiders an bombardiers can get through that gap, I tried blocking it off and the orbs are still getting through one stem wall layer then scaffolding where Ive built steps up onto the poles and even another stem fence against the stairs!!!!  Whats the use of building a fence if these buggers can get through it, not just one thick but two?  Or is only the plank fence suitable for fencing ..I mean a fence is a fence and surely the wood stem is stronger than planks?