I guess my question is how are you rewarding? Are you giving him treats or just praising him? I stopped giving my shepherd puppy treats relatively quickly. Once he got the point, I started praising him without treats and only gave them every once in a while, and I eventually dropped the treats completely. I probably stopped giving treats within two weeks or so. I still praise my 7 year old golden retriever when she goes to the bathroom. I usually praise her if I ask her to go and she does, or if she does it in a weird place upon my urging.
Forrest - GSD 9/1/2016 - 5/14/2017 RIP
Brooklyn - Golden retriever 1/30/11