Tense, being over border (2,4)
I believe the answer is:
on edge
'tense' is the definition.
(thesaurus)
'over border' is the wordplay.
'over' becomes 'on' (I've seen this in other clues).
'border' becomes 'edge' ('edge' can be a synonym of 'border').
'on'+'edge'='ON EDGE'
'being' is the link.
(Other definitions for on edge that I've seen before include "Tense and irritable, very nervous" , "Cliff-top walker may be" , "All agog" , "Twitchy" , "Anxious, nervy" .)