Hello, I am new to this forum so let me start off by saying Hi.

I was recently lucky enough to be able to adopt a 5 almost 6 year old male GSP that is fully registered. This is my first GSP to own. He has a terrible problem of wanting to try and hump EVERYONE. How can I handle this?

Obedience and exercise

Welcome to the forum. I'll bet he's a crotch sniffer also.

Next question, he will fetch for me all day long in the house but when he gets out side you can't get his attention at all. It's like he's a different dog inside and different outside

FF.

You should join a gsp club, navhda, etc to help with the dog. Also, searchng the forums will help a lot at most of the questions have been asked before.

You have his undivided attention inside. Let him run around for a while before the fetching starts. Small steps.

Welcome to the forum.
To start with... a few words stand out in your post.

"recently, adopt"
"6 year old"
"first GSP to own"

GSP's can be incredible dogs, but they need structure and exercise. They also need to be challenged mentally and really thrive in a family environment. Sounds to me like he's an older dog that hasn't had a lot of obedience training and you guys are still getting used to each other trying to figure out who's in charge!

Work with him on obedience commands and give him lots of exercise. Not just a walk around the block, a good off leash RUN for 30 minutes to an hour several times a week. It will be best, until you get real good control on him to find a place like a baseball field or a large fenced area where he can run and you can work him without the chance of him running off.

Unless you know or have a way of finding out what his command set was before you got him, you're going to have to basically start over with him, but since he's 6... he should be able to give you some indication of what he knows and you can just work on reps with him.

Sounds like you need to start with "HERE" and "OFF"(for the humping thing). "here" is very easy to put on a dog with just a CC and some yard training (even on walks). If you have access to an ecollar, "OFF" is a pretty easy command to teach and enforce quickly, but if you don't have any experience with a ecollar, I would find someone who does to help you.

I would work all the basics like "HERE", "Kennel", "OFF", "WHOA" and get him used to some structure before even thinking about Force fetching him. In fact, once you guys figure each other out, you might not need it as he might come around on his own.

Just be patient with him and "teach" him what you want. Most GSP's are very biddable, pick things up quickly, and want to please.

Good luck.