HELP!!!!!! Urgent please Questions

Hi Everyone,
Please can I ask for some help......
I regard myself as an experienced dog owner, having owned many large breed dogs in the past.
Having just lost our Bernese Mountain Dog, we did a great deal of research and decided to buy a pre bred 3 year old male GSP.
We brought him home this morning.
He is a wonderful dog, very large, soft mounted and great around the children...
However, he is displaying extremely dominant behaviour, mounting everything except my husband, including the sofa, but more worryingly myself.
I am currently pregnant and he can't be in the same room as me without leaping on top of me and humping.
I love this dog already, but he's pacing and whining, mounting and generally just unsettled.
Is this just first night nerves?
Would castration help in anyway?
We are trying to assert our authority and although he obeys basic commands, he is still pacing and just rather unsettled.
We've been for a walk, fed him etc...what are we doing wrong?
Will this behaviour change?
So sorry, I just turned to you guys as experts for some help.
We have an appointment in the morning with the vets, I just want to do right by this pooch.
Thank you in advance for any help you can offer, it honestly will be extremely gratefully received.
x

Sounds like the dog as only known mating not a family life, he might of gone from one bitch to another without a break.

Thank you so so much for replying.
We did initially think this, as the previous owners wanted no money for him, even though he comes with his paperwork and GSP incredible lines.
They gave the reason for rehoming him as the fact that they have had to recently house him outdoors at their landlord's request and he wasn't happy being an outdoors dog.
They specifically wanted us to rehome him (a family) as opposed to him get into the hands of any breeders.
So I don't know, there seems to be something not quite right about this dog and I'm not sure I can put my finger on it - I think this may be more than first night nerves somehow....

Humping is rarely anything to do with dominance but more as a result of over excitement, or anxiety and is used as a displacement behaviour. You've had him not even a day yet so I certainly wouldn't worry about asserting yourself over him or anything, just give him time to settle, be gentle with him. I would guess his behaviour is as a result of the recent upheaval he's suffered. If the behaviour is a learnt one then castration is unlikely to make a difference, and I'd give him time before making any rash decisions. Instead of getting frustrated or thinking the worst of the mounting behaviour, instead everytime he attempts to mount you or anyone else simply get up, walk out of the room and leave him for a few minutes to settle down. If he persists use distraction instead, show him a toy or even do a small training session with him to engage him in other ways and give himself something else to focus on. That in turn will help build a solid relationship too.

Thank you so much for your help, that really is fantastic advice - I'll start straight away.
Thank you a million times x

As said already - he'll be a 'Bonny boy' at this age and he's just in his new home. Give it a bit of time.

What do you mean " there`s something not quite right" , is it just the humping or are you suspecting the owners did not tell you the truth.

The first thing I would do is RING THE BREEDER OF THIS DOG!, you said you have all his paper work and his breeder should be on that, I assume you did not buy from the breeder but the previous owner..........what a shame these people did not contact the breeder before re homing him.

Anyway the breeder will know this dogs lines, how they mature and temperament, and so on, and if you feel you cant handle this dog , it would be only fair to inform the breeder, who may help with re homing!

I the first thing you need to understand is this behaviour is NOT dominance, and castration may not help infact it could make his behaviour worse, this may be a learned behaviour, in other words he has never been told not to do it, the previous owner may have just allowed him to hump everything.......my boy is a humper, he can be a nightmare at times, but I am constantly on top of it,

If this behaviour is a learned on (they hump when excited or they simply just like it) you are going to have to re train and redirect his behaviour, it not going to be easy and he may always be a bit of a humper, so you need to ask yourself are you up for the challenge, given your pregnancy and commitments to it.

I have also heard that some dogs can behave oddly around pregnant woman, I don`t know if there is any truth to this, its just something I have heard.

It could all be down to a new home and his needing to settle in (ask the people you had him off for the truth) because this could be why they got rid.

For now what I would do is remove anything that he would hump (toys/cushions/beds) and attach a long line to him, keep treats around everywhere and if he starts to hump, pick up the line, remove him from the item ( even you) and ask him to earn his treat,

It might be beneficial to introduce the NILF way of training, (google it) in other words he needs to earn every aspect of attention.

i.e.... feeding him, he has to sit first, giving him a toy, he needs to sit and wait, if he is calm he gets attention.

Refrain from any form of excitable play, this may set him off,

As you can see there will be a lot of work to turn this behaviour round, but is this the only worry you have, be honest with yourself, and try and get in touch with the breeder.

Some really good advice here. I would add - try to make sure that he does get an adequate amount of exercise, as GSP's are quite a high energy breed.