Not likely to change horses (6)
I believe the answer is:
stable
I believe this is a double definition.
'not likely to change' is the first definition.
(I've seen this before)
'horses' is the second definition.
(I've seen this before)
(Other definitions for stable that I've seen before include "String may be kept in this" , "Lasting" , "Equine housing" , "Animal accommodation is steady" , "Settled; animal shed" .)