Coflein (thanks Kammer for bringing Coflein’s existance to my attention) says:
Small hillfort on rounded hillock, two lines of defence circle the hillock, the outer consists of an earthen bank and an external ditch. The inner defence is a heavily robbed stone wall, between 4 and 5 metres wide. The entrance ramp cuts both defences on the SE.
No mention of the strange, big, white and distinctly out-of-place stone. Nor of the chevaux-de-frise (sp?) on the NE entrance.