Stop king and fool becoming bound together (5-4)
I believe the answer is:
close-knit
'bound together' is the definition.
(I've seen this before)
'stop king and fool' is the wordplay.
'stop' becomes 'close' (I've seen this before).
'king' becomes 'k' (abbreviation for king in chess).
'and' means one lot of letters go next to another.
'fool' becomes 'nit' (I've seen this before).
'close'+'k'+'nit'='CLOSE-KNIT'
'becoming' is the link.
(Other definitions for close-knit that I've seen before include "Tightly bound together" , "Bound by strong ties" , "United or joined together - with wool?" , "Bound together as by family ties" , "No tickles, being woven tightly" .)