Justify is related to Explain. Explain is related to Understand. Understand is related to Clear. Clear is a synonym of Pass. 
you would Fence because Defend. Defend is a type of Argue. Argue is a synonym of Debate. 
Justify <--RelatedTo--> Explain <--RelatedTo--> Understand <--RelatedTo--> Clear <--Synonym--> Pass 
Fence --MotivatedByGoal--> Defend --IsA--> Argue <--Synonym--> Debate 