Years working the borders of Kansas. Years and years (5)
I believe the answer is:
yonks
'years and years' is the definition.
(I've seen this before)
'years working the borders of kansas' is the wordplay.
'years' becomes 'y' (abbreviation).
'working' becomes 'on' (on can mean working or activated).
'the borders of' says to hollow out the word (remove centre letters).
'kansas' with its middle taken out is 'ks'.
'y'+'on'+'ks'='YONKS'
(Other definitions for yonks that I've seen before include "Slang for a long time, ages" , "Long time (informal)" , "Ages (informal)" , "Many years (slang)" , "An age" .)