Live somewhere in Herts, but watch out! (6)
I believe the answer is:
beware
'watch out' is the definition.
(bewaring is a kind of watching out)
'live somewhere in herts' is the wordplay.
I cannot quite see how this works, but
'live' could be 'are' ('they live' means 'they are') and 'are' is found in the answer.
This explanation may well be incorrect...
'but' acts as a link.
Can you help me to learn more?
(Other definitions for beware that I've seen before include "Steer clear of" , "Be alert for dangers" , "Archaic injunction to be careful, look out" , "Archaic warning to be careful, danger ahead" , "Stay alert to danger" .)