It takes a special kind of person to take on any rescue dog but especially one of the bigger breeds as you have to rely a great deal on what you've been told by the Rescue Society.
Unfortunately, not all the groups are as honest as they could be so you really are taking on an "unknown" entity.
When approaching a rescue organization, it may be an idea to ask

1.  If & how was the dog assessed and by whom, what were their qualifications?

2.  How long was the dog assessed for, what conditions and more importantly,
     are there any problems that you should be aware off?

3.  What kind of follow up support do they offer after rehousing the dog?

A genuine organization will be only too happy to provide you with the answers to the above as they have the dogs best interests at heart.

It has also been brought to our attention recently that some groups are now charging a fee which is non returnable should you be deemed unsuitable for a rescue as well as charging a "donation fee" on receipt of a dog. These groups should be avoided as genuine rescue's should only charge once, that charge being a "donation".

Unfortunately, not all Rescue Societies are what they seem so it is important to satisfy yourself as to the competence of such groups.

Should you go ahead, here are some helpful hints that may be of use to you when you receive your new found friend.

1.  Don't just get your new friend & rush out leaving him alone.

2.  Don't throw a party for your new friend, he may be confused and 
     need time to settle in.

3.  Introduce friends, neighbours & relatives over a period of time.

4.  Take time to get to know your new friend.

5.  When your new friend arrives home, always supervise meetings
     with children and other family pets until you feel you can trust him 100%.

6.  Always remember, your new friend has a past and although he should
     have been thoroughly assessed, some things may worry him. Should this
     happen, a little reassurance may help to convince him that there is nothing
     to worry about.

7.  Some new friends when they go to a new home act like they've always lived
     there whereas, some may be nervous. Allow for this and with some peace &
     quiet as well as some reassurance should help settle them.

8.  Try to get him into a routine as soon as possible & stick to it.

9.  Enrol your friend in a local dog friendly training class as a trained dog is a
     happy dog. You'll build up a bond & learn to respect one another as well as
     having fun.

10. Shepherds are very intelligent, think up learning games to both occupy &
      stimulate his mind. A sad sight is a totally bored dog.

11. Visit your local library & borrow training books, you'd be amazed at how 
      much fun you can have and yes, you can teach an old dog new tricks!

12. Any problems you may have with your new friend should be able to be
      overcome with patience, thought & a little consideration, don't give up, 
      persevere.

13. Don't be afraid to contact the rescue society should you have problems as
      a responsible society will be only to pleased to help.

To make sure your of to a good start, try to take the dog when you've a few days off so you have plenty of time with your new friend.
It should be noted that when taking on any dog but more so the rescue, you will need a lot of time, effort, patience & understanding but the rewards are just unbelievable therefore, think seriously before making any final decisions.

Helpful Reading

The Dog's Mind   Bruce Fogle

I'm Nobody's Dog
Dog Days
Two For Joy
How To Own A Sensible Dog
all the above by Joyce Stranger

Joyce was our inspiration when we were having such a hard time with Corra & on the verge of giving up.  As well as being a wonderful author & qualified trainer, she is a genuinely nice, kind, caring person.  Her battles with her naughty GS bitch are legendary but with alot of kindness & understanding, Chita came good in the end.