
Castration will only affect things that are sexually driven. A lot of mounting behaviour, especially when there is no in season bitch around is behavioural and not sexual, so would not be affected by castration.
If he was well behaved in kennels it might be worth asking what their routine and management of him was that is different to at home and give that a go.
Distraction and training is the best cure for unwanted behaviour, teach him things that are incompatible with mounting behaviour so that he can be distracted into a behaviour for which he can be rewarded, as often it is about attention.