Fence is a synonym of Security. Chain can be used for Security. 
Gain is a synonym of Realize. Realize is related to Think. Think is a synonym of Suspect. Suspect is a synonym of Imagine. 
Fence <--Synonym--> Security <--UsedFor-- Chain 
Gain <--Synonym--> Realize <--RelatedTo--> Think <--Synonym--> Suspect <--Synonym--> Imagine 