Thank you Tenderfoot for this answer to a problem we were searching on Google - have joined the forum especially to show appreciation
Just to give the background to what is happening here our daughter and husband have a Jack Russell dog that has been neutered and a spayed Jack Russell cross.
We have no problems in our home environment or when walking our five month old Jack Russell dog - he did go through play humping other dogs but from socialising seems to have learnt this is not acceptable behaviour.
Although young the mature neutered/spayed pets have accepted him as pack leader.
The mature dogs are very well trained with our son-in-law a very dominant Alpha male.
Initially our puppy was friendly to all humans and without fear but then went through a period he seemed afraid of most male humans. We wonder if this was not exactly fear but wishing to avoid confrontation.
We are feeling that Scamp approaching six months is now feeling more confident and not prepared to be dominated by someone showing Alpha characteristics!!! Excited to see the other dogs yesterday, at our daughter's house, Scamp peed a welcome on my son-in-laws shoes. He adores my son-in-law but in the excitement of what was happening we did not give this potential problem serious consideration (or the right solution) at the time.
We know this forum , and of course our UK vet, are in favour of neutering. As stated on my profile we previously owned a Cairn Terrier and also had Papillons and never needed to have a dog neutered because of behavioural problems.