seperation anxiety/shy of people

There will be others along with a lot of great advice. This dog is still not used to her new home, not sure of its place, and can take a long time to adjust. In the meantime let visitors be aware of her fear, dont push anyone on her and maybe give visitors treats to lure her to them on her own terms.
As for the seperation anxiety I would do a search here on i-dog to get some great insight, but like I said others will be along shortly!

I also have a shy dog. Since you don't know the background on this dog, I would give him some time to adjust. Also, for now, don't let anyone approach him, let him meet people on his own.

hello!,
 our Kiara had terrible seperation anxiety when we got her...crating was out of the question,as was leaving her alone...destroyed our bedroom in a 10 minute time period when i had to run out..

 we had to let her get used to her environment and after a 3 month period she was much better...i also had to tire her out and then leaver her alone for short time periods and increase them gradually...we also got her a companion,and by that point ,the troubles with seperation anxiety were gone.

 We also have another dog who is super shy of strangers...he is my wifes dog and wont even come near me unless the other dogs are around..when the other dogs are with me,he will lick my face and even sprawl out on me and sit next to me...pretty strange...would like to know how you make out..

this is one of the most common problem with large breed dogs over the age of 2 when they are brought into a new home. as was said before let people kno the dog has a fear of meeting new people within his home. when people come in dont allow them to walk towards the dog or talk to him because eventually fear can turn into biting. the dog is uncomfortable with people so should work on being socialized outside of your home. the walk is key though establish dominance before attempting to correct any other problems. trust comes with him seeing you as a leader. when you come home after being out try not to give the dog too much attention because it actually makes the dog feel more like they own YOU instead of vice versa. wait till he calms down before showing affection and help him to understand that no matter who is coming in that being anxious will not get him any positive attention. have one or two different people help you work with the dog at first to avoid overwhelming him, you dont want him to feel cornered. then once he becomes more comfortable you want him to understand that the PERSON is dominant to avoid any future problems, have the dog show his belly. but as i said the walk is key, before attempting any of the you want the dog to be fairly warn out, so that he'll easily give into you, be persistant and assertive. but show its ok to trust you, no children or large men, and no hats or facial coverings on any new people you introduce.

Thank you all for replying.  These are some great ideas and a place for us to start.  I have sent emails out to other places but this is the first place that has replied.  Thanks so much.  I will let you know how he does.

you want him to understand that the PERSON is dominant to avoid any future problems, have the dog show his belly.

 
This dog doesn't need to understand people are dominant he needs to understand they are safe.  I would not require this dog to give up his stomach at this point.  It will make the dog more uneasy, and there really is no point.

 the walk is key though establish dominance before attempting to correct any other problems. trust comes with him seeing you as a leader. when you come home after being out try not to give the dog too much attention because it actually makes the dog feel more like they own YOU instead of vice versa. wait till he calms down before showing affection and help him to understand that no matter who is coming in that being anxious will not get him any positive attention. have one or two different people help you work with the dog at first to avoid overwhelming him, you dont want him to feel cornered. then once he becomes more comfortable you want him to understand that the PERSON is dominant to avoid any future problems, have the dog show his belly. but as i said the walk is key, before attempting any of the you want the dog to be fairly warn out, so that he'll easily give into you, be persistant and assertive. but show its ok to trust you, no children or large men, and no hats or facial coverings on any new people you introduce.
 
Oye!!!  Excuse my lack of manners, but what a load of crap!  I work with a gsd rescue and we routinely place large breed dogs over the age of two without issues.  This dog is new to your home, so she needs some time to settle in and feel SAFE.  You can facilitate that by providing her with structure that is firm yet fair.  I agree that strange people should NOT be allowed to approach her.  Let her go to them when and if she's ready and they should totally ignore her even when she approaches. The MOST anyone should do is slowly place a palm up hand out for her to sniff.  The world is FULL of men, children and people wearing hats, so for heavens sakes don't exclude those folks.
 
Benevolent leadership (being alpha) and establishing dominance are two very different things.  The first is what you need to strive for.  I'm not a trainer or a behavoralist, but I can take just about ANY dog, regardless of size or background, out for a walk and correct ONLY with my voice.  I've been volunteering at the local shelter a few days a week since we moved and taking the dogs out for walks.  The ACO is constantly warning me off dogs that just flat don't like people.  They like me just fine.  They behave for ME just fine.  On a flat collar, with no leash corrections, just voice commands and VOICE corrections.
 
Last week I saved TWO dogs from the kill list.  The ACO has asked me to come and work with them a bit so they CAN be adopted.  Remember, I'm not a trainer, or a behavorialist.  Just an old broad with a ton of dog experience under my belt...and a huge love for dogs.  They sense that love and respond.  Far better than if I hauled out the whips and chains.
 
And, in the wild, showing the belly is a display of total submission......it can be VERY scarey for the dog, so with a fearful dog I'd sure not ask for that.

My dog is timid of strangers (but getting better), so I understand what you are going through.  Glenda has given some really good advice.

Have you ever heard of NILIF?  It is a non-violent, non-confrontational way to establish leadership.  Fearful dogs need strong but kind leaders.  They need to know they can trust you, or it will only add to their anxiety.  Establish a routine and stick to it.  Dogs are more comfortable when they can predict their lives.  Sally THRIVES on routine.

Start doing basic obedience exercises--sit, down, etc-the sessions should be short and very upbeat--lots and praise, etc.  Setting the dog up for success will up his confidence.  "Smart toys," like treat balls, can help to up the level of confidence as well.

Never, EVER force the dog into meetings with strangers.  This will only frighten him more and you want strangers to equal wonderful things as much as possible.  For every negative experience with a stranger he has to have a thousand positive ones.  Also, make sure that if he displays fear, you do not coddle him--no "it's ok boy, it's ok."  He will likely see this as praise, and think that he is right to be afraid.  Praise and encourage progress, and ignore fear reponses.

Above all, do not make the mistake that I did and expect too much to fast.  The dog must go at his own pace.
 
ETA--please do NOT alpha roll your fearful dog.  This will only be terrifying to him and possibly dangorous to you.

Also, when you feel the time is right, you may try giving him more exercise.  I will admitt that I don't know how much exericase that St. Bernards need, but exercise seems to relieve some stress in dogs as it does people.

be careful with how , where, and what time of day you excersise the dog due to the density of its fur and its lack of the ability to sweat, they can get very sick if they overheat

Give this guy some time to adjust.  Find out what makes him calm and give him his own space (a crate or a bed area) and don't disturb him while he's there.  He'll get reassurance that way.  Dogs don't always respond the way we want when they get to a new place.  There's a thousand new smells, new routines, new people, new interactions that they have to learn. 
 
Imagine if you went to bed in your home and woke up in china...you wouldn't know the language, the customs, how much money things should cost.  You'd be a bit lost and a bit timid.  That's how your dog feels, a bit overwhelmed and lost.
 
Once the dog gets used to the structure that is provided, he will feel a bit more ready to meet outsiders in the ways mentioned by previous posters.  Don't force the issue as this is a good way to instill fear.  No rolling, no forcing, let the dog progress at his own rate.  Positive reinforcement every time he does something more outgoing.  Once he starts to trust build upon that trust.  You'll be glad in the long run that you did.