Exposed as a lie; tacked (6)
I believe the answer is:
nailed
I believe this clue is a double definition.
'exposed as a lie' is the first definition.
(I've seen this in another clue)
'tacked' is the second definition.
(I've seen this before)
(Other definitions for nailed that I've seen before include "Fixed with a pin" , "not allowed to escape?" , "Fixed with metal spikes" , "Fastened with spike" , "Fixed - caught" .)