Hi there - my male Dalmatian (Captain) was exactly the same. He would not go anywhere but in the yard at home.

I also started with commands in the backyard - "Go and do your thing" whenever he went outside to do "his thing", and slowly but surely whenever we went for a walk, I would keep suggesting that everytime he sniffed a tree or stopped. Eventually he got the idea ....... and now he is a typical MALE dog.
It did take awhile tho ....... only when he was over a year old did he even consider doing anything outside his yard.

We even went away overnight, and I swear he did not do ANYTHING the whole time ..... so we rushed home afterwards, and he ran out the back and just went "mad" so to speak.

I now have a female Dally (Ruby) who does NOTHING outside the yard when we walk, but when we go away, she happily copies Captain. We also taught her the "go do your thing".

Aren't dogs just wonderful ........... make you really use your mind, and then worry you out of your mind too!!!