Hi ginge. I saw it as a double definition. Pinto fold - (Pinto horse- fold-enclosure for animals), so "Pinto fold" is stable, as is firm- Pinto fold Firm
Aha! I'm sure that's it ginge.
Nice but I would never have solved it without crossers , so not quite as satisfying as fieryjack @11 - one of those where the solution seems obvious and you get the penny drop when you parse it.
Cheers ab, similarly I took firm to be gang/association but now you've pointed it, your parse makes your clue better so my apologies for not giving it the appreciation it deserves.