Would YOU be willing to pay to have a behaviouist/trainer see him? You said you were willing to buy him back, perhaps if you explained to the owners that you are really very concerned that a pup of your breeding is having these problems and would like to pay to have him professionally assessed for your own peace of mind they would agree. Just a thought.

I realize that it is obviously an environmental problem as his litter-mates are fine, but it might be a way round the impasse.

What has annoyed me is that they had the money to take him to the vets but did not consider that that money could have paid for a behavourist. She is now saying that she had him done as she had no intention of him being used at stud which I suppose is a fair comment but he is still far too young for that op. Apparently he growls at then when they tell him off. I am going to phone her and see exactly what she is talking about, if this is an excuse to get rid of him then I am happy to have him back and try and sort him out.

Hope you can get this sorted out as he is young enough to unlearn this behaviour fairly easily.

However, if the owners were silly enough to ignore your advice on castration one wonders if they will listen to anything

Nothing to do with the dog, but I can't see how a properly worded and signed contract can fail in court, even a verbal contract can be binding if made in front of independant witnesses.