Sandie
>Would casteration solve this problem?<
Davdee
It might, it's well worth a try but neutering does not guarantee anything, it just makes some things more probable. Very often we overlook normal dog behaviour, some of them display both homosexual and cross species sexual behaviour, mounting peoples legs can be a problem if the dog is not obedience trained so it's hardly surprising your dog is getting attached to the bitch.
Personally I don't see anything which suggests any veterinary problem and just because a dog does something we don't understand it by no means suggests a trip up to the vets is required.
If on the other hand it will make you feel better by paying a vets visit I suggest you do that. I would STRONGLY suggest that you do not use a vet who is tied in with any behaviourist, they are commercially involved and the vet refers you to one of these people who in turn charges a fee, usually around £100 and is able to tell you no more than I have.
If it were my dog I would simply interpret it as normal behaviour for that dog in its interpersonal relationship with the bitch and get him neutered. If it did reduce the behaviour it would be a gradual process over around six months.
Because the dog has learned to relate to the bitch as he is doing it is unlikely it would stop the behaviour completely but it might reduce the intensity and might stop any increase in the behaviour.