How do I get a new day care 11 month old GSP to stop barking the whole time he is at my place?

GSP's are very high strung dogs so I feel your pain. Patience is needed and also time for the dog to feel comfortable at your home. Also, the GSP needs lots of exercise, really lots of exercise, so short walks aren't enough. Get a slip lead to control the dog if you can, forget harnesses as most don't work. Is there dog park close by that you can take the dog to and let them run or if you have a fenced yard that can also help. Best of luck and I hope the dog calms.