Registers to prevent the advance of appalling behaviour (6,2)
I believe the answer is:
checks in
'registers' is the definition.
The answer and definition can be both to do with communicating as well as being verbs in their -s form.
Perhaps you can see a link between them that I don't see?
'prevent the advance of appalling behaviour' is the wordplay.
I cannot really see how this works, but
'advance' could be 'in' (synonyms) and 'in' is located in the answer.
The remaining letters 'checks' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
'to' acts as a link.
Can you help me to learn more?
(Another definition for checks in that I've seen is " Chickens (anag)".)